Saw that thread pop up again, just as I had the girlfriend's 1993 Borrego in for some work.
Sadly, the BB area is pretty chewed up by the chain - I rode it hard when I bought the bike new at 17.
?2K1 6279
I just bought a 1986 Timberline with a very hard to read serial: I'm reading 1Z070329.
There's a completed listing for an '85 Timberline on eBay showing GT4K1377.
This looks very good apart from some blemishes on the stem and the missing pedals.
Mine came with an XC pro rear derailleur for some reason, most had complete XC expert.