I use Atlas roller bearing trucks (70T or 100T depending on the application) on all of my MTH and Lionel 2-rail conversions.
Why fuss with taking trucks apart to retrofit with scale wheels when you can use Atlas trucks? They come with a plastic adapter which allows you to mount them to other mfr's railroad cars. In some cases, like Lionel PS2 hoppers, the adapters aren't required as the 2-rail trucks are a direct replacement for the 3-rail trucks. Plus, Atlas offers scale wheels in 33" (50T & 70T) and 36" (100T) diameters.