The interference is primarily at the sway bar, though I have seen them rub the frame at the rear. This is with stock offset S truck 4x4 wheels. You might be ok with a rwd offset, though you might need to check for fender opening clearance, as the wider wheels and rwd offset will alter the scrub radius. I think you're definetly on the right track test fitting. 31x10.50s should be easy to find used, they were stock size on the ZR-2 S10s, though some years did use a P rated 265/75/15. Unfortunatly, that size has gone obsoltete, and, as you mention, is very hard to get. We run into problems with that size often, especially when we get an S10, early '90s Ford, or Colorado with the off road package. Those all use that size tire, and there's just not much available. but 31x10.50x15 is very close, maybe about a half and inch taller and maby .20" narrower.
