Another point regarding MPC's modification of the postwar AAR truck tooling to use the new needlepoint axle design, is that they also filled in the cavities more in the two simulated hollowed out ares of the truck sides. Why they did this I don't know; I'm assuming that they felt with the delrin plastic that the postwar truck design needed more structural reinforcement. When they came out with the Simington-Wayne trucks, they did have those cavities completely hollowed out so that you can see through them (like you can on real freight trucks) but these cavities were much smaller than those on the AAR (and other far more common type of roller bearing trucks).
So apart from the fast-angle wheels, new plastic uncoupling tab & locking arm, and the aforementioned more rough-looking surface, this is another key spotting feature to differentiate between the postwar and MPC AAR trucks.
