I bought a pair of American Models' Bettendorf trucks (part #820) to be used as the trucks for each of these cars for the time being. To determine the thickness of the bolster, I put the frame on the trucks in the approximate position. Prototype drawings indicate that the top of the car stood at 3' 10-3/8" above the rails. I measured the car and concluded that it was a scale four inches too low. This allowed me to build up the bolster area. I glued a 20"x24" piece of 0.040" styrene on the area where the mounting screw is going to be. An extra 0.015" was needed to come up with the four scale inches. I cut a piece of that material that you can see in the photo below. The ends float above the car's sides. I am getting ready to glue it down. This makes the piece bend down, which kind of mimics the prototype. In the photo you can see that I have already glued the center section of that part and then used my drill press to drill the right sized hole for the screw you see in the background.
Next, I glued the "flaps" of the bolster down. After that I used the screw to "tap" the holes.
The screws needed to be cut down (a good pair of heavy wire cutters will do the trick, although it is tough on your hands). I tried not to drill the hole through the top of the car. It's not that big of a deal, because the wood decking will cover the hole later on.
The next step is to mount the couplers. I had built the end sills without regard for the couplers, on purpose. I used my Coupler Gauge to mark off the amount of material to remove from the end sills.
The next photo shows a coupler installed. I had to cut the end sills and part of the center sill. This took me several relaxing evenings to accomplish that for all the cars. Since there is no real material to put a mounting screw into, I just glued the coupler box onto the car. If I need to replace the coupler, I don't expect it to be too arduous to remove. By the way, the wide-bodied wheels will be replaced by code 110 wheelsets soon (A.M. uses code 124 wheels).
I couldn't wait to test them out on the layout. Here my NW2 is pushing them down a siding. The cars tracked fantastically. The lead shot really adds to the weight of the cars. I ran them around the layout with no problems at all.