30x9.50x15s fit very well without rubbing, and you can use a 15x8 wheel with 3.5"-4" backspacing (3.5" is correct to OE) without issue. I woudl suggest using wheels speced for an '87 or earlier 4wd 1/2 ton Chevy. If you go with aftermarket wheels, order the caps separatly so that you can get 4 closed caps, otherwise the wheel company will ship 2 closed and 2 open caps.
One thing, the 205/75/15 is a bit undersize for that truck. The correct modern equivalent would be 215/75/15.
