widest rear wheels on box caprice?

[87_9C1_89]

I have a couple of boxy 9C1s and am considering doing a LS3/6L80e swap on one of them. With all that power, I want to get as much grip in the rear as possible. What are the widest wheels that will fit the rear without requiring rolling or any other such modifications?

I thought I remembered someone over on the old 9c1.net forums having 10" rear wheels, but not sure...

Anyone know? And I'm assuming 8" wheels are the widest you can go on the front?

thanks.