Disclaimer: circa 10 years ago I bought a Trek 750 with the same paint scheme, in similar conditions. At the time, I identified it as a Trek 750 from 1996. I kept the frame and fork and the bottom bracket, bought a used rear wheel with 9 gears complete with derailleur and shifter, as well as a super cheap (and heavy) triple crankset. It was a fantastic bike, I used it as a multiday touring bike (sort of adventure bike, road and gravel) and as a commuter bike (quick and relatively light). Stolen from my cellar, so I hope someone else is enjoying it.
As mentioned in the comment, the chainstay bridge looks fishy (that much rust and 2 holes?). Be ready to say goodbye to this bike soon.
However, if
- the fork is smooth, and it is not bended;
- the pedal cranks are not wobbling
it is still a good base. Two properly mantained wheels and a new bottom bracket (and cranks and chain) and the bike will be super smooth. But I would be worried about the bottom bracket shell. Maybe it disintegrates if you try to remove the bottom bracket.
Some ideas:
http://blog.peterlombardi.com/?s=trek+750 (it is an older model, different frame but similar configuration regarding fork thread, eyelets and so on...)
some picture to backup my claim
a lot of rust, never had structural issues
your flag has weird scratches. Note the very famous sunrace (?!) cranck I installed