All very interesting. I do have these pieces with AAR Trucks. The trucks look rough as the tooling was wearing out by this time. I guess they did cast the trucks after 1970. Also some late 60's pieces. Notice the odd cast wheels on the tankcar.
I have a number of those early MPC cars with the AAR trucks as well. I suspect that the tooling may not have been worn out per se, (the tooling was less than a decade old and molds used for plastics tend to last longer than those used for die-cast) but perhaps when Lionel modified it for the new needlepoint axles surfaces in the tooling got roughed up somewhat in the process, or perhaps it was an early production problem with the delrin plastic combined with the injection molding process that resulted in the trucks looking a bit rough and the oxidization on the trucks; usually the residue comes off with a shot of Pledge and a rag.
Needless to say, I really wish they fixed that early problem with the plastic trucks and kept using those carryover postwar AAR trucks or used a new truck design similar to the ASF ride-control type type trucks LTI came out with after 1989 instead of those very obscure Symington-Wayne trucks.
