Seth Gartner provided this info after a quick google search turned up this snippet from a conversation on trainorders.com:

The track geometry slug, NS 34, originally started off its life as Norfolk and Western SD35 No. 1530, delivered in 8/65. It was demolished in a wreck at Lynchburg, VA in in 5/76 when it hit a standing ballast train at track speed. It was rebuilt by the N&W Roanoke Shops and out shopped as N&W RP-E6 (Remote Power - EMD 6-axle) road slug No. 9921. This unit and sister 9920 (rebuilt from a wrecked Erie Lackawanna SDP45) were each mated between a pair of SD45 masters. The 9921 was renumbered to N&W 9951 in 5/81.

Following the N&W and Southern Railway merger in 1982, the slug became NS (N&W) 9951. It was retired and placed into storage in 10/89 and then leased to the Wheeling & Lake Erie Railway in 5/90. It was returned from the W&LE in 9/92 and once again retired and placed into storage.

In 7/94, the NS Roanoke Shops began work on the 9951 to convert it for track geometry operations. Work on the unit took place over a period of five years when things were slow in the shops and it was finally released as NS 34 in 7/99. The slug car body had been rebuilt with taller areas at each end, the fuel tank had been shortened, the traction motors had been removed with track measuring devices added to one truck, and a generator had been installed in the carbody to power the measuring equipment. The unit was painted in NS tuscan red and lettered in dulux gold.

That above post was from Chris Toth. The link to the original discussion is:
http://www.trainorders.com/discussion/read.php?2,342706,nodelay=1

First things first, I needed an SD 35 to gut. A friend donated an old Athearn Central of Georgia SD 35 to this project.
 

Let the demolition begin! 
All lights, horns, hand rails, fans, windows, and antennae were removed. 
Next the dremel tool, exacto knife, assortment of files and a table top belt sander were needed
to remove all of the body parts.  This included various exhaust vents, boxes you name it.


The entire body was milled down around the bottom.  While this one time slug was raised it still is not as tall as it was when it was an SD35. Interestingly the early version of the is locomotive did not have a cab, the newer version does.  I liked the look with the cab better so that is the version I am going to recreate.


Both the front and rear noses were ground down around the lights, and grab rail holes. 
The edges of the nose were filed to appear sharper on the corners as well.  The front nose drops a little just in front of the cab.  This section had to be ground out to match the #34. A small piece of sheet styrene was molded in for the sloop.


Behind the cab, the body slopes downward as well.  This had to be removed with the dremel tool.
There were several exhaust vents that had to sanded smooth.  As you can see  from the photos the shell has huge gaps in it now.  


New sheet metal.  Now that all of the sections have been removed, we can begin scratch building the new body sections.

Starting behind the cab, sheet styrene was cut and fitted for the new body look. .020 Sheet styrene was used to build the new sheet metal. The rear side panels were layered with styrene to make sure the future vents would be flush with the panels.  


Slowly but surely the old Central of Georgia starts to take on the shape of the prototype Geometry Locomotive.  The next step is to fill the cracks and holes with modeling putty.  Once dry the lengthy process of sanding and filing begins.  Followed by another layer of modeling putty.


This will be followed by the removal of all striping and lettering.  A quick coat of primer was used to start filling in the sand marks as well to help highlight the uneven places.  It will take several coats of primer before the shell is ready for the Burgundy Paint.   As you see in the picture once primed the shell was sanded again, then another layer of modeling putty was placed in the low areas.  This was followed by another sanding and another coat of primer.  The primer was sprayed on lightly so as not to fill in the details. 
 

While the shell was drying I moved on to the walkway or deck frame.  Having lowered the shell, the frame no longer fit.  I had to remove the same amount from the battery box area on each side of the cab.   I did this by removing the entire area first, then cutting the battery boxes in half. 
This was done so as to keep the flooring intact on the top of the battery boxes.
As you can see all of the grab rails were removed prior to cutting the battery boxes.   Now the one row of battery boxes can be glued into place. 

Once the shell and the shell decking are put together, additional sanding and filling needed on the shell. 
With each coat the shell begins to look better.   I have decided not paint the locomotive until the engine and frame are all customized to fit together.  This is done so as not to mark up the new paint job.

The various vents were added last so as not to fill up them up with primer. The notch was also added into the slope behind the cab. I missed this completely

 

The first attempt to alter the frame or chassis ended up by cutting to much of the frame and ruining it altogether.  That particular Athearn frame had been customized to start with so it was weakened before I ever started.  Starting over I used an Atlas SD 35P frame donated by Mr Bob Williams again!.  Thanks Bob!.   Much cutting and fabrication was needed to make this fit under the shell correctly. It would of been much easier to simply remove all of the weight thus only making one cut along each part of the chassis itself, however the more weight the better.

The fuel tank was cut in half which is a delicate job being that it was molded metal to the chassis.
Using sheet styrene a new end for the fuel tank was made. The Geometry instruments were made by cutting one side of a ladder off then gluing six black rubber contact tabs onto the open ladder rungs. The instrument box on the side frame was fabricated out of existing F unit spare parts.

The ultimate goal is to house a small dcc decoder in the rear of the body. I would love to be able to install sound, but that may be out of the question. 

To get the shell and the frame to fit together several small cuts to the shell inside the cab has to be made.  The entire cab interior was removed to allow the gears to swivel.  Once the shell and frame mated up nicely many of the shell detail parts could be added.  Several of the top parts were made from scratch using bits and pieces of other parts left over from past projects. The only remaining parts left to glue into place are a set of rear vents, the window wipers, along with the decking rails.

Using model masters bright white spray paint the #34 top gets two coats of paint. I will let this dry for several days before taping it off to paint the burgundy.

After taping off the top portion of the shell, the remaining portion was painted.  I sprayed two light coats, and then one medium coat.  The paint job came out very nice.  The scale coat 2 paint over the model masters did not present any problems.  You can save yourself a lot of headaches by applying light coats at first.  Eventually to get a good shine you will have to apply a medium coat. 

After painting all of the handrails they were glued into place. The side rails that go to the cab from the front steps had to altered, as did a couple of their placement holes to make up for the lowered height. Using Microscale NS decals, along with NS OCS decals from "Shell"  the shell really starts to look like the prototype. Just a few small details remain, along with replacing the scratch built ac unit with one in production currently, that is if I can find one.  Also this loco is wired for lights so I am still looking for some small spots that go along the side rails. 

Taking the NS 34 out for a spin after programming the decoder to respond to #34. It ran like a jewel around the Southern Exchange layout.

Ok a couple folks and have written to remind me that these are not powered.  My bad, this one does! 

Parts List to date:
Athearn SD 35 High Nose
020 and 010 sheet styrene
Detail Associates Grille Set  'GE; C32-B (existing parts were cut to fit)
Detail Associates Grille Set  GR 2713 (existing parts were cut to fit)
Model Masters Bright White spray paint.
Scale Coat II Caboose Red spray paint
ShellScale Decal Kit  #161
Microscale Decal kit 87-1225


 

Scratch Built List -
Cab ac unit was built from layers of then sheet styrene.
top rear muffler unit was made from left over piping kit parts.
Antennae in front of cab were made from left over F unit parts, These parts were altered to look similar to the prototype.
Small raised vents on each side of the rear were made from sheet styrene, then covered with mess from grille kit (detail associates). 
Six black electrical tab covers and regular small ladder, the geometry instruments were fabricated.