The most basic reason a finish is applied to a guitar is to protect the wood. There are a lot of very good products available now that should be just fine. Browse around at StewMac to get some ideas.

You could probably find out what the original material was, if you want to be authentic about restoring your guitar. Myself, I would want the best stuff available now rather than using what was state-of-the-art almost 30 years ago. Unless you find that it is worth a huge amount of money, I think you are likely to keep it for sentimental reasons. That frees you to fix it up the way you want it, without being limited by resale considerations.

To paraphrase your sign-off, you should be allowed to focus on the joy you get from this guitar.

Enjoy! :)
L