Alot better info can be had with some digging around here but here's the short list.
1. check out the SJR lifts. Lots of guys around here have 'em, and I've seen one up close and it's good stuff.
2. Find yourself and old set of Peugot wheels off of an old 505. 14" or 15" depending on preferance. Or you can use 6 lug Toy, Izuzu, Nissan, Chevy..... (the list goes on) wheels. The thing to remember is the old Soobs are 4x140 lug spacing. You can redrill wheels, or the hubs and add studs. Either way you use two of the studs to line it all up. There are instructions on here somewhere. (Check out the USRM as well, it's the repair manual section of this forum, there is an off road mod section in there)
Tire size is gonna be up to you. Remember we don't really have gearing options so alot of guys seem to not like going over 28". I like mine around 26" to 27" to keep some of the low end, and it's a full time wheeler. Only pavement it see's is to get to the trails.
All a prefererance thing. And what kind of wheeling you plan on doing.
Wanna stay slow and techical. Stay a little smaller on the tires. Gonna just play on forest roads and more open areas and dunes, and want it mainly look cool doing it. Go a little bigger. There are still a few decent off road tire options in the 27" sizes being made.
3. Have fun.
These things are a blast off road and the looks you'll get out on the trails by other wheelers will be priceless.
It's always more fun to use the "wrong" tool for the job.