The Grand Wagoneer is a great vehicle. I own a '85 and even when it was stock I could go places others could not.
The AMC 360 is a strong engine, might be worth your while to try and re-build it. I had to replace mine because it blew 2 pistons off the back. Total cost to get it back on the road was ~$3,000. I replaced alot of components on it while I was at it though. The block cost me $1,800.
As far as the body is concerned, open the hood and check behind the wheels, infront of the firewall. This is a great place to pack in mud and it never comes out. If it still has the roof rack, make sure it is sealed. Check for leaks on the headliner. Should look like it is sagging, water marks, soft to the touch, exc. The problem is if the roof leaks, it will soak the carpet and then rust out the floor boards. Make sure you fold the rear seat forward and look under it. Rust spot.
Other problems that I have had:
Seat belts, wont retract- Soluton: Replace with manual
Window falls of the track- need new worm gear.
Rear Window won't go up or down- Replaced safety switch.
Wanted it bigger- The only company that I could find that would offer a lift was BDS. They gave me a 4" and I can fit 33X9.5. Anything bigger than that and it gets hung up on your fenders.
Parts and Supplies- Some parts are easy to find, others you have to go to the dealer. This is a website of someone that can mail out some FSJ parts. http://www.oly4x4.com/
By the way, It is verry dificult to rebuild a FSJ overseas, as a result of poor Italian driving.
4 Jeeps, '90 YJ, '85 Grand Wagoneer, 2-'72 Wagoneers.