Unless you made all of the tapes on the same deck, or at least with the same azimuth, it is going to be difficult to get the most from your tapes without spending quite a lot of money (say $1k or so).
I suggest you visit the Electronic Services Labs (in CT)website, and check-out their Nakamichi pages. This will put my comments into perspective. This would be your high-cost alternative.
If your tapes are from a variety of sources, including pre-recorded, I would e-pay a low mileage Nakamichi deck, have it serviced for playback only, and have at it. This is the low cost alternative.
Nakamichi hit its pinnacle in terms of best parts and high-tech by the LX series. Many compromises were made by the bean counters as Nakamichi began to compete in the mid-fi arena. I submit a properly aligned and serviced LX-3 would do the job, unless of course you want azimuth adjustment, in which case the price goes up even if the overall quality is _slighlty_ compromised (effecting longevity).
-Kurt