According to the wheel fitment sticky at the top of this page, my 87' Z28's factory wheels are 15X8 with 4 1/2" backspacing. If I have the inside of the wheels widened (behind the spokes) Front & Rear 2" and add a 2" spacer , this should move the inside edge of the wheel back to the stock location (clearing all suspension componets). This should move the outside edge 2" out and should be flush with the rear fender. The front fender lip would need to be pulled/extended about a 1/2".
Well, what do you think, are my figures about right?
The tires im wanting to use are 295/50/15 on all 4 corners, these tires are 26.7" tall, 11.6" wide, and has a 5.8" sidewall. If the fenders are all rolled, I don't think they would rub. http://ssl.delti.com/tyre-pictures/Toyo/ProxesST.jpg I'm just wanting to put a bigger contact patch on the ground.

I've done a few searches on this subject but found nothin conclusive. for any constructive info on this subject.

 

this is the best pic i have of my buddies 91. hes running some draglites at 15x10 with a 5.5 backspace. looks pretty tight. IIRC the wheel is pretty darn flush at 5.5 BS.

I dunno about the 27" tire though, might be a little tall. I am babysitting my buddies 85 while he is in iraq. he has 5 spokes with some really tall truck tires on the back. looks kinda goofy.