Another tip - most higher quality bikes from the 70s and 80s had shifter levers on the downtube, where they are in the Prelude and Peugeot. Lower quality bikes had shifters on the stem by the handlebars. If I remember correctly, the 70s Grand Prix had stem shifters. It was right on the borderline between between a cheap bike and a nicer bike.

Downtube shifters can seem pretty inconvenient until you get used to them, so make sure you can live with that before you buy the bike. Your other alternatives are to find a borderline bike like the Grand Prix, or you can talk to somebody at the co-op about converting an older bike from downtube to some other type of shifter.