|I assume you used the term "frame off" in quotes because you know that these are unibody vehicles and it is not possible to remove the body from the frame...
With that said, it probably is not worth the cost to pay someone to do such an extensive restoration, as you would not likely recoup even a fraction of the cost if you ever wanted to sell it. My personal advice would be to look for a low mile garage-kept example and have a full maintenance update performed. Even if you drive the car a bit you will still be way ahead of the game price-wise and have something all original.
If money is no object and you have car of particular sentimental value, then there are a number of outfits that work on the Z-marques and will do everything from original stripped to bare-nothing restorations to ultra high performance mod packages. We saw this with the 240Z's a little while back, and the same folks would undoubtedly do this on a Z32-- for the right price (which is undoubtedly in the stratosphere now).
However, as we are seeing, fewer people want to rebuild the z32 engines for some reason (I suspect that there have been a lot of reliability issues in the last decade-ish), but at least you can still buy a brand new transmission from Nissan. Unfortunately, there are a load of parts that are discontinued and finding them in new or like-new condition is a bit of a scavenger hunt.