Just buy mine and be done with it!
You should pay attention to which TC they have. That really depends on what you want it to do though. If you're looking at one with a QuadraTrac, you might want to make sure it has the "low range" mod done to it. The NP229 is a full-time TC and has a vicious coupler in it that can be problematic if you want to off-road the thing. The NP208 was a good choice. Also, most of the 4wd systems (it may be all, but I hate to speak in absolutes) are vacuum actuated, so make sure engine vacuum is present at them. You don't want to be like me and get the thing home only to discovery you don't have 4wd!
Make sure the rear window works. Those things are NOTORIOUS for not working right, if at all. Actually the same goes for all the power windows. Gauges also fall into this category.
Hopefully the owner will have knowledge (and be truthful) of the engine maintenance. Not keeping the oil changed properly can lead to problems with the FSJ.
They came with several engine options over the years. The 4.2 I6, the 4.0 I6, a 360, and the ultra cool 401.
There were (to my knowledge) 2 sets of gearing that came in the D44's. The towing package came with the taller gears, so look for that.
The FSJ is a plush ride in stock form. It is also very capable. People think they look huge, but they really aren't.
