I suspect the "older" refers to the trucks with somewhat wide bolsters to accommodate three-rail wheelsets. The "newer" trucks have a narrower bolster (still accommodates three-rail) but looks closer to scale width on the car; no "clown shoes" as Joe F would say. I have a couple of the "newer" freight trucks and the narrower bolster makes a noticeable difference.
EDIT: Your trucks should fit with no problem.