I don't think the MTL (56000) is a clone of the USRA twin. For starters, the stirrups are different, the slope sheet angles are different, and the MTL car is missing the characteristic sill gussets that the USRA car and clones were built with.
The MTL car measures out to a
30' 32' inside length, compared to the USRA at 30'6"
The MTL sides are 7' high, while the USRA design is 7'5"
So even though the cars are similar in many overall areas, I think they are fundamentally different.
To put it another way, if MTL's goal was to make a USRA clone, they did a lousy job.
(re-posted from another thread).I like the theory that Bryan B posted in that Bmann USRA 55 ton thread, that MTL stretched a two bay to fit the offset twin frame.
That said, the MTL rib side is close to some real cars built in the 30s and 40s, VGN had a class of twin hoppers very close to the MTL car, I'll see if I can dig up some online pics.