Last I heard, O scale trucks will fit under O scale cars.
Not quite.
Atlas don't model the bolster on the frame; their trucks have a deeper section instead to compensate. Probably makes it easier for them to supply the same car as either 2- or 3-rail.
As I have replaced MTH trucks directly with Atlas (for the rotating bearing caps) then same applies, so I doubt that these true-scale trucks will fit Atlas or MTH, but they may well fit Weaver who did things properly in the bolster dept; & these trucks would be a significant improvement over the Weaver plastic ones.