Yeah buddy, if you're wanting to upgrade engine, might as well go V8, that's what i did, 350 v8 LT1 camaro engine, and a nv4500 transmission, solid build, strong build, and a nearly bulletproof transmission at that. a 6 cyl is the stronger stock jeep, but its not THAT strong, hardly strong at all actually...
But if you are heart set on a 6, get-r-done.