Welcome to the club aj. And congrats on your find. However, and this is all just my honest opinion. $1000.00 is a bit high for ANY 6x6 that doesn't run or move. (As it sits, I wouls offer $5-6 hundred.) Especially a trail boss. Getting it to run is one thing, but getting it to move is another. The biggest downfall for the T-boss was probably the transmissions. (And still is since they stopped making them back in the 70's. I think it was the 70's.) Richard's relics will sell you a used one if you need it, but his price is high, ($350.00 when I inquired 4 years ago.) and you will probably have to rebuild it anyway. Some of the members here probably have spares. There are also two different styles of trannies. Simply put, "Old" and "New". The only difference is the braking band system, and you really won't know which one you have until you open one up. At this point, there is no need to get to deep into it. We'll cross that bridge later. You mentioned that you have the parts needed (Coil?) to get it running. See if the seller is willing to let you install for testing, to get it running and see if you can make it move. The only things you can do to check the trannies without the boss running is to check the movement of the laterals/sticks. Push them all the way forward, and pull them all the way back. Note as to wether they both move the same distance in both directions, and the resistance you feel at the end of travel in each direction. They really shouldn't move much more than 5-6 inches from full forward to full rear position. If movement is the same, or very close, in both trannies, they are probably worth reworking. And there is a fill plug on the inboard sde of both trannies. Pull the plug and stick a piece of stiff wire or wire tie down inside and check the fluid condition. Beware of metal flakes and/or dark/burnt fluid. The biggest failure in the trannies is probably the braking bands. Which can be relined if you have the newer style. Also grab the input shaft(s) and give them a good push/pull. Check for slop in the bushings. And check to see if the input and output seals show signs of major leaking. If so, it could mean input/output bushings are worn. New bushings can be made if need be. I'm not trying to discourage you, or talk you out of buying it; just trying to give you a quick "T-boss 101" briefing on what might be ahead of you. I do hope things work out for you, and you do end up with a 6x6 that you can work on and enjoy. If you need any other help, I'll be more than happy to give you a hand. Just post or PM me. As far as registration goes; that differs from state to state. Some do, some don't require it. You'll have to call your local DMV or DNR/Game warden.
It's all just nuts and bolts.