The JR-XT rims have a lot of offset, the bearings are at the inner edge of the tire.
Most current truck rims would make it narrow, and may not fit. I think the 5 link rear would be the worst, not sure without checking.
The mountings are the same as far as I can remember, not counting the new CR, just need enough offset so the tire clears everything and it doesn't end up real narrow.
Good luck, I'm working on restoring my original very early Losis too.