I picked up a 2002 Trek 820 off of ebay, and it arrived today. Apparently the 38-21 gear combo has proper tension, and a straight chainline to run the bike as a singlespeed. I took it to the LBS to get brakes, a new seatpost, new grips, and to get the rear wheel trued. I will go pick it up after work tomorrow.
I now also want a stem closer to the bontrager sport on my 4500, and a similar seat for the 820.
I also wonder if I will have to replace the chain more often as there isn't a way to keep tension as it wears.
I am also wondering if anyone has converted one of these to a "96er or 69er" style, with a 29er up front and a 26er in the rear. I wonder how much the combination of bigger tire and fork, with the angle change would effect handling.