I have come across a 91 Jeep Wrangler with a blown 6 cyl. engine. I want to replace the engine. What year engines can I put in this Jeep without alot of rework?

you can put the stock motor back in or you can get a stroker that uses the same block & head. there are kits that will allow you to put chevy v8's in her. i would suggest sticking with the stock block just build her up.
check ebay & search "4.0 stroker". give you a rough idea

6 cyl 4.0L Jeep engine is more than adequate for the YJ Wrangler, especially offroad; IMO there is no need for installing a V8 or any other engine. The expense of swapping your 4.0L for a different engine is difficult to justify. It's difficult to beat the original 4.0L engine that evolved during the late 80's and early 90's. Economically, it would be best to repair the existing engine, if possible. If it isn't possible, I'd recommend replacing the engine with another 4.0L Jeep engine.

So, what's wrong with the "blown" engine, specifically? Can it be easily repaired?