SunTour ratchet barcons are best in class. I put them on a 2 x (ultra-)6 transmission on the Peugeot, with a Shimano Titlist front derailleur and a SunTour Cyclone II rear, and they are a delight to use. Judging from lever throw, 7 speeds in back should be no problem, and I know from other experience that 3 in front is no problem on the other side.
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"Far and away the best prize that life offers is the chance to work hard at work worth doing." --Theodore Roosevelt
Capo: 1959 Modell Campagnolo, S/N 40324; 1960 Sieger (2), S/N 42624, 42597
Carlton: 1962 Franco Suisse, S/N K7911
Peugeot: 1970 UO-8, S/N 0010468
Bianchi: 1982 Campione d'Italia, S/N 1.M9914
Schwinn: 1988 Project KOM-10, S/N F804069