I checked the wheel driveshaft length on the lst2, not much more than 1/4" more in length so not worth the time.
Yes, I have seen people use the big cen genesis arms and driveshafts on the savage.
Here are a few pics with wheels on. I got measurements for the Redcat rampage body and it is 10.25" wide. So I think at 18" width now it will look a bit too narrow. Does anyone know how much wider the xl axles make the truck? Look at the pics it does not look like 1/2" per side, maybe less than that?