I assume you're looking for something with rigid forks, are you going to fit drop bars?
If so, have a look through the manufacturer archive: http://www.retrobike.co.uk/gallery2/v/M ... r+Archive/
I would look for something from 1990 to 1993, before front suspension and suspension corrected frames started appearing and something with a short-ish top tube to work better with drops.
For example, from recollection, Marin and Kona tend to have a fairly long top tube for a given frame size, whereas Orange were a bit shorter. You'll probably still want a short reach, high rise stem to make an MTB frame work with drops though. There's a thread here for drop bar-ed MTBs: http://www.retrobike.co.uk/forum/viewto ... op+bar+MTB