Looks like a 1982 728 to me, should be long gone regardless. In a hot market, where turds go for $125, a real steel frame Trek? Wow.
Time spent trying to identify the exact model first, just gives your competition time to scoop it up.
Grab now, study later.
Hopefully you are loading it into your car right now.
If not, when it is reposted in a few weeks, assembled, cleaned up, fresh tires, and with a $700 price tag, the seller will list exactly what it is, give good size info, and more.
Bar cons, 531 frame, center pull brakes, Duopar RD, bottle cage braze ons on the bottom side of the DT = 1982 728
Here's a real nice 1982 728 that sold recently on ebay for $810 plus shipping, a much crappier one went for $1100, but I would consider that sale to be an outlier:
http://www.ebay.com/itm/49cm-50cm-52...p2047675.l2557