I finally got around to completing the build of a GM&O 35200 series Auto Car. The starting point was a HO Scale Speedwitch Kit that included a Branchline Body and resin ends, doors, parts and decals.
I was fortunate to have picked this kit up from Ed Hawkins who also help me obtain General Arrangement and Brake Arrangement Drawings from the National Museum of Transportation in St Louis. After looking the drawings over 
I decided to scratchbuild a new accurate underframe. Along the way many items were scratched or modified for this car to better match the general arrangement drawings. An item that stalled my build were the somewhat unique10 rung ladders. Friend Jim King of Smoky Mountain Model Works came to the rescue and designed and printed ladders from the General Arrangement Drawings using an SLA 3D printer. The Side and end grabs and Equipco Brake Housing is also 3d printed by Jim. Attached are a couple of photos of the build showing the underframe, sides, ends and a couple of the finished car still to be weathered. Note that the underframe side sill is built up of two C Channels as per the drawings and the crossties nest in the c-channel.  A note on the end ladders is that the right-hand stile is a flat piece of steel and not L-shaped as the other side. The flat piece has bends in it that allow for it to be attached to the ends. Look closely and you can see this captured as per the prototype. Car was finished with Vallejo Acrylic Paint and given a coat of Pledge/Future Floor Care before the decals were applied and then a final coat of Model Masters Flat was applied.
A fun project using old and new materials and methods to construct
George Toman