look at the engine mounts.. this will give you some clue on the job they did to put that engine in... also the radiator.. how rigged up is that.. second.. go to the tranny/transfer case.. what are they? will they hold? how are they put in the jeep and hooked to the engine.. then the axles.. but start at the engine.. you dont want someone else's nightmare.. and looking at the small details will tell you alot.. the welds.. the wiring... things like that..
Beyond what everyone else has told you, I suggest you fill out your profile soon, it makes it easier for us to help you. I think they covered everything that I KNOW to look for [img]images/graemlins/wink.gif[/img] Hope it works out for ya!!!
Be sure to go over the frame carefully. Look for soft spots and cracks. If the frame is soft then it isn't a very good deal. Make sure and check around the steering box, that is a place that problems pop up often.
And Welcome to the board