I love old Treks from the 80's and late 70's. For years were both my choice of new bike, then solid value on used bike. Even the cheapest, lowest end Trek from that period is something that has good bones and can be a fantastic ride, since during this this period, Trek's focus was on producing good frames that could be configured to a user's taste/needs.

The internal cable routing through the stay was pretty common. Something you should do is get a "step down" ferrule for fitting the cable housing to where it emerges from the stay. Not always strictly necessary, but keeps things clean and keeps the cable from rubbing/sawing on the hole.

Classic Americana there. I just wish it was 10 years ago when you could pick these things up for pocket change....