I have been using Intermountain wheel sets in the original Lionel trucks and they seem to work well. There was a post in I believe O Scale Resources where someone popped out the bearing inserts and installed a small shim behind the bearing to help center the wheels. The contributor used a small piece of styrene punched out with a hole punch for the shim. I believe the shim was .030 inches thick. I have been assembling the truck without the shim and it seems to work OK. Wheels are a little loose but so far they haven't come out. You have to cut off the 3R coupler with a Dremel and a cut off disk.