I know before the 4.0 there was a 258 straight-six...I dont know who made it though...I'm answering your rhetorical questions because I dont think this idea is so sacreligious...There was a thread a while back in the big bolts forum about putting a diesel in a medium duty bolt, and some of the ideas there were even more outrageous...International T444s (can you say "powerstroke"?), 4 cylinder detroits, and Cummins diesels in a bolt...it makes a Jeep 4.0 seem downright at home under a chevy hood