When I designed the TopGon (BLMAs first freight car, I hadn't designed the BLMA trucks until the second freight car (PS-4000)), I recall we used a slightly different version of the Atlas 100T truck, one that had just come out on the Evans gons. It had a shorter coupling distance than the other 100T Atlas trucks. I believe this version is now standard... but it's something to look out for if you're swapping trucks from older or different cars