I recently purchased a new mountain bike. I bought my last one in 1998, and mountain frame geometry has changed a lot ever since.
So, since my old bike fit me right, I took three measurements from the old frame:
c-t seat tube
effective top tube
standover clearance

With these three measurements, and considering what I was looking for (more standover clearance than my old bike had, for example) I got a pretty good idea of what "modern day" frame size would be good for me.

Maybe you can do the same in reverse to find the right vintage frame.

hope it helps,
JEB