Tire Size Question on 84 K10 w/ 4" Lift

[SourTooth307]

My K10 currently has a 4" lift with 35" tires riding on the original 15" stock wheels. I feel that they might be too big because they rub when you turn the wheel fully left or right. My friend is junking his 88 Ford Ranger w/ 2" body lift which is currently sitting on 31" brand new off road tires and I'm being told I can have them for nothing. Both are on a 15" wheel so I know I can mount them, but would my truck look stupid with the smaller tires? My current tires are dryrotted by the way so they really should be replaced but I just don't have the loot to go out and drop almost $900 on a new set of rubber. Anyone with pictures of a K10 (really any full size rounded line) with 31's on it I'd love to see them.