I'm contemplating finding a 4.0 from a 91-95 jeep. A pretty common thing is to take the crank from the 4.2 and put it in the 4.0 to make a 4.5 stroker or bore it .060 to make what's called the "torque monster" 4.7 stroker.
Or, put the 4.0 head and top end onto the lower end of the 4.2 which is a complete bolt on procedure, giving you a 10:1 compression ratio. And basically it becomes a fuel injected 4.2.
My uncle has a late 70's cj5 I believe with a 327, and that's a mean little motor in it. There's plenty of options out there, I just need to choose one and go with it. And find myself a new frame being that the jeep has at least 6 cracked spots that have been welded already but continue to break.