I agree with most that either size you listed is pretty negligible in both gearing and ground clearance effect. The ~8% increased width of a 265/75 would be more of a worry for steering parts stress than the ~3% increased diameter is on the drivetrain, and really wouldn't be a game changer in...
Looking forward to your build! I remember coming across your 80 for sale on Craigslist and watching your walk-around video a bunch of times. Had planned on giving you a call but didn't have the funds in order. Best of luck with the new rig.
You'll probably want to take this to PM. The current owner has the truck listed for sale but you replied to the previous owner's thread from 2012. Those not looking at the dates will assume it's sold.