I also have a TH54 that I am trying to get up and running. When I bought mine I went by what the guy told me and told him I would buy it if he brought it to me which he did. As it turned out he knew about as much about it as I did which was nothing. I was real busy when he brought it here and didn't have time to really go over it for a couple weeks and when I did that's when I found out that it wasn't as sweet a deal as I had thought. Oh it had a lot of accessories alright just none of them were for this machine. I only got one tool holder that would fit the old lantern style tool post, no milling table attachment like I thought he said it had, no center or follower rest and on top of that some of the change gears were missing or broken. The machine itself was in pretty good shape and it did have a 3 jaw and a 4 jaw chuck along with a drill chuck but no key.
From what I've seen most of these things people just bought and didn't use them much and they sit in a garage most of their life and in those cases just a good cleaning and oiling would get you going. It's hard to tell about a machine until you actually get it set up and running. Just look at the bed and look for dings and bangs, broken teeth in the gear boxes and that all the feeds move freely. The bed will mostly wear mostly in the last 4 to 10 inches or so before you get to the head stock look for wear there. Look also for bangs and dings there too sometimes people let the chuck get away from them when changing them out and they fall on the bed.
The good thing about these things is that pretty much anything that goes wrong with these lathes can be fixed. The bad thing is that used parts are really over priced and sometimes hard to find when you really want them. I've spent more on the parts that should have come with the machine than I paid for it in the first place and I still have a ways to go before it is a completely working machine. These machines are pretty noisy when they are running but most of that noise is coming from the gear box and the light weight material that the gears are made of. When running it will sound like crap but listen for any unusual bumps and thumps which could be broken teeth on a gear or a bearing getting ready to take a dump.
Hopefully your machine will have at least the basic tooling and hopefully a QC tool post with tool holders. If it has the lantern style it's still ok but make sure the tool holders will fit the tool post A center rest would be nice and maybe a follower rest too because they are $150 or more each, on e-bay. most will come with a 3 and 4 jaw chuck along with a drill chuck and live and dead center. All these things on e-bay cost more than they are worth but that is the nature of the game.
