One other item of note (I don't have the Culotta article, so I can only guess he has a sophisticated method of what I'm about to describe) is that the IM car sits roughly 6" too high because the portion of the carbody bolster, on the frame/bolster molding, is too high. I basically start with the round hole and carve that entire section off, and file it down until it's dead level with the frame member surfaces. That plane will intersect the sloping surfaces of the body bolster just a tad outboard of the frame edge. There will then be a rectangular opening here.

I then add a .010 styrene piece that I've carved a round hole in, on top of that flat surface. The hole only needs to be roughly the same diameter as the tapered part of the body that the truck screw goes in. When I cement that piece on, I then use an old Delrin truck frame to press it down and encourage it to cure flat and level. (You of course could use any truck frame, as long as it isn't styrene.)

I now use Evergreen .010 x .188 strip for this, but I made earlier ones from sheet.

And, it wouldn't hurt to add some styrene outboard of the bolster to take care of that part of the underframe that's just flat missing. To me, if I can't see through that part on the layout it's good enough.

And, yes, I prefer to start with this IM car because it's otherwise about as good as we can get.

Ron Merrick