Re: engine swaps
Putting any thing other than another 2.5l in your jeep is not a simple task. Yes, there are engines that are easier than others....but none of them are simple 'bolt ins'. Issues to contend with....
1. Computer wiring.
2. Motor Mounts.
3. Fuel Lines.
4. Adapter plates.
5. Emissions laws.
6. Can your driveline handle the bigger engine?
Rule of thumb...do NOT put in an older engine that what you jeep is. Even if the state you are in does not have emissions laws....it will soon. Even California is happy to let you swap in a newer engine...as long as it is done so that it retains the stock confiuration for the veh it came out of....in my case, my 84 CJ is becoming a 94 Chevy PU...as far as smog is concerned.
If you want to replace a FI engine with a carborated engine....then you are asking for more problems than you realize....and you don't know what your doing...
Now...to answer your question......Almost any engine can be swaped in...some are better choices than others....your best bet is to stick to the common ones because you will find more info and parts.
All Small Block Chevy's...Engines are cheap and there is plenty of them.
The Buick and Chevy 4.3 V6 is also very popular and gives you more room.
Ford 302 is slightly smaller than the SBC and about 100 lbs lighter.
The new Hemi is starting to be a much sought after swap...but engines are hard to find.
You will want the doner veh...cuz you want the engine, wiring harness, computer, and in most cases the tranny...not to mention all the misc pieces of wiring and hw that goes with it.
And this is not something that you do in the driveway on a weekend....I have been working on mine for about 1 1/2 years now....with luck, I crank it up next weekend.