How large of a tire can you mount on a stock 4x4

[Lugnutt]

I have a 72 chev K10 with stock suspension. When I first bought the truck I used to run 12.00x16.6 tires and rims (no height labled back then). They only rubbed a little when backing up with the wheel turned just so (no problem). For the last few years I've been running 31 x 11.50 x 15 with no rubbing at all. What would be the tallest tire I could reasonably assume would fit my stock truck without too much rubbing? Would 32 x 11.50 x 15 be too tall? I know the rim offset has something to do with it also... any spec's on that too?

Thanks for your input