Re: Will 17\" Avalanche Wheels fit a 68 Chev Pickup
Well, they'll probably fit for the most part.
The Avalanche wheels are probably "6x139.7" which is a fancy way of saying 6 on 5.5". They should be for 14mm studs and your 68 should have 7/16" studs. There's quite a difference in diameter (like 3mm) but as long as the Avalanche wheels have conical seats you should be alright.
The backspacing will be the killer though. It'll probably be around 5" of backspacing. I doubt your 68 will like anything more than 4".