It appears that no one has said this yet. For your 1980s Trek, make certain that you have measured the outer separation between the rear dropout eyelets, because that must be matched to the rack that you choose. Today's rear triangles can be ~10mm wider than those of the 1980s, depending on how the rear wheels were configured.
Also, the rack does more than support the panniers. Do you want to mount a rear light on it? Some models have a tab designed for the T-style clip mount rear blinkie. Do you plan to mount fenders as well? Make sure that your attachment plan provides for the fender stays.
Good luck. PG