That looks like a really nice jeep. The short front cj5s are pretty tight for engine swaps. Although I've seen Ford 289 cid V8s, Chevy LS, and even a big block chevy swapped in one without an over abundance of custom work. A small Block ford 289, 302, etc. or a Small block Chevy should swap in easily. With lots of aftermarket parts available. The main difficulty would be drive shaft angle because of the short wheelbase. And maybe clutch linkage if you keep a manual.