On proto I'm pretty sure 36" is the correct diameter for all of them.
However, the older MTL passenger trucks were designed back in Kadee's (MT's) 33" fits all days, so they were designed for 33" wheelsets. I don't know if 36" wheels "work" in these trucks - hopefully someone will comment. ;D
Of course the new MTL HW passenger truck uses the new MTL 36" wheels.
IIRC, MTL uses 0.540" axles, which FVM does offer in various wheel sizes.
Mark