You may be right about the SIS, but I don't recall any Trek bikes made prior to 87 that said SIS on the frame...for that matter even after 87, but I could be wrong-it wouldn't be the first time.SIS is Shimano Indexing Shift, but he says it's got Suntour, so it doesn't sound like it's in original condition. And while some steel Treks are valued as touring bikes, this isn't one of them. Which brings me back to my original comment - a run of the mill road bike old enough to have 27" wheels is probably not worth much.
I learned my lesson years ago with cars that I sold that I should have kept, and knew I should have kept! So I won't sell any of the bikes I have; I did sell one about 2 weeks ago, but that one I really didn't like it a whole lot, and that was a Nishiki Olympic I sold to a friend who is having problems running after years of running and he really liked the looks of the bike a lot so I parted with it. Then back in 77 or 78 I sold a 76 Trek TX900 with Campy Record stuff I bought new because I needed a better car! But that was youthful stupidity. Otherwise I normally keep all the bikes I've bought over the years. But bikes do take up less storage space then cars and cost less to maintain!I still regret getting rid of my old Univega Gran Premio. The frame was of Japanese manufactured Tange steel. It had a beautiful sparkly blue paint job. It had Suntour derailers with these funny down tube shifters that when you shifted the rear derailer would automatically trim the front. I sold it to buy parts to build up the colnago frame that my brother gave me. Which ironically I later turned into a fixie. Yes I kept all the parts.
I regret getting rid of all my past bikes. Never again.