I know that a 15x8 with 41/2 backspacing will fit under my 70 chevelle with a 27560 tire, does anybody else have any idea of how wide I can go,and what tire size? I am looking at the weld draglites I was wondering if the 15x9 with 51/2 backspacing would fit, with no problem or even a 15x10. I need to get the bigblock to hook up, please help.

You can fit a 15x10 with a 5" bs and a 296/50 15 or a L60 15. Getting bigger tires wont necessarily get you "hooked". You need to get traction bars and some suspension work to do that.

There was a thread in the last 2 weeks that showed a homemade tool for checking wheel/tire clearance.

Like he said above, it take much more than tires to make a Chevelle hook up.