Can someone please help me, I have a 1964 chevy II, stock 10 bolt rear and want to run rally wheels, but I am having a hard time finding out the width of rim and tire and backspacing I need, I want to go as wide as possible without modification. THANKS IN ADVANCE!  

Without having to modify the wheel wells, the widest you'll probably be able to go is 8" or 8.5" wide wheels and tires.

The backspacing question is a tough one for me to answer. On that oen, what you might want to do is find your local wheel shop, and talk to them abotu measuring for what backspacing you'll need. But a factory Rally Wheel should have the proper backspacing to fit your Chevy II.