While, I've never been one for wheel spacers, excessive strain on the studs is enough for me to say no.. Why use a spacer though when you can get a good aftermarket option with the correct offset? I bet money you can use an 8" wide wheel on a KJ given the correct offset of the wheel. Stock offset is +41. If you wanna run 'em, do it! I'll just never risk it.
For clarity purposes, I thought we were referring to bolt on spacer
adapters, like what I put on mine. My stock 16x7 Renegade wheels (they're color matched and I wanted to keep them, which answers the question why) have a back spacing of 5.5". My 1.5" adapters now gives them an
adjusted backspacing of 4", which is a pretty popular consensus around here. The wheel studs will have NO more strain on them than what wheels having an actual 4" of back spacing would put on them, that's just plain ol physics.
Now, if you're talking about those slip on frisbee spacers, then yes those can put more stress on the studs.