neither is easy to do on a small budget...at least not to do properly.
350 Chevy's are a dime a dozen though and have umlimited aftermarket support. a 350/TH350 (or SM465 if you want a manual)/NP205(from a ford truck for the proper axle drop) would be a pretty bulletproof combo...
Your dana 35 axle that came stock in the YJ probably wont last long though with that kind of power.
1985 CJ7 Project
Phase One :
5.3L Vortec/4L60E, Moser axles for AMC20, Twin Stick'd Dana300 - Completed
Bedliner, Rollcage, Seats, BESRK Rear Bumper w/ tire swing, Soft Top, and a few other goodies - Mostly Complete
Waggy 44 front, Scout D44 Rear, 4.56's, ARB's (F/R) SOA with YJ Springs, 35x12.50x15 BFG MT - Not Even Close to beginning
Also a mostly rust-free 1970 Scout 800A That I'll get to start working on someday...
Chrome won't get you home...BUT Rattle Can Black may just get you back"