Which Nakamichi to choose?

This will provide a good test of the system sensitivity and your hearing. Get two Walker 1/2" resonance control discs, $50 each.
Place one very near Nottingham motor without it touching the motor holder, place another one on top of the deck where the transport is located. You should hear a slight improvement in clarity. If you don't - there will be a work to do. Nottingham Spacedeck is a very emotional, dynamic and quite quiet turntable, some people prefer it to much more expensive tables. Also, when recording from it, I can clearly hear differences in pressings when listening to the Nak. I can also compare cables and phono stage power cords this way.

@orpheus10 What are the odds I looked at the pic of your deck, nice looking deck btw, and there is one listed! Looks like a good buy for $550 if I was in the market I might snap it up.

https://www.audiogon.com/listings/lis93faf-sony-tc-ka3es-tape-decks

It is a good buy if you can still replace all the rubber in the deck; that gets old.

Ok here is my advice on what Nak to get. Get the Dragon or ZX9. another consideration is the 682zx. From what I have read it has a more solid and robust transport than it predecessor the mighty Dragon. You are probably going to have to pay a qualified tech( not just an arrogant overconfident know it all) but one who really  knows the machines. It will cost you. It doesn't make sense to pay $500 to get a lesser Nak up and running to spec when you can find one of the 40,000 Dragon non working been in the closet for 30 years  eBay auctions. But if its just for non critical playback  go for any of the later economy Naks. Maybe all that is needed is a belt.

I heard that Dragon requires more maintenance, and I bet 682ZX records better. ZX-9 is extremely rare and very expensive, great machine, but 682ZX has a classic Nakamichi sound which many prefer. 680ZX is probably the best value overall, though I heard that the bass is not as good as 682ZX's. Can't verify that. ZX-7 is fine too, getting rare as well. I took a look at ebay, prices went up significantly compared even to the last year.