I don't know if all Dodge axle flange to rear end housing offsets are the same.
I would check the offset of the axle to the end of the rear end housing, and compare between the truck and the car..
If the drums from the truck are wider, then the drum may hit the backing plate before it seats on the axle flange if the offsets are different..
That is where I would start.
my signature lines...not really directed at anyone in particular..
BE different....ACT normal.
No one is completely useless..They can always be used as a bad example