The late model aluminum rims will fit earlier trucks, but you have to turn about 1/8" off the widest part of the rear brake drums and grind a bit of metal from the the rod ends. On some trucks, a bit of metal must be removed from the steering knuckle to clear the wheel.
Make sure the front wheels are pushed all the way back to the rotor, or you could cinch up the lugs and bind the wheel at an angle= wobbly wheel. It is a very tight fit at the center circle in the front wheels, but the wheels will fit with a little bit of work.
Dave