I sort of did that, but with a heavy stove pipe frame from an Armstrong 3-speed. I used a Sturmey AW (wide-range 3-speed) hub with a long axle and 14-16-18-20 Cyclo cogblock and an early Campag. Record rear derailleur with a downtube-mounted old style Simplex shift lever. I tucked the 3-speed trigger under/inboard of the left brake lever on the drop bars, to facilitate double shifts. Transfer that whole concept to any proper lightweight slack geometry road frame (my 1959 Capo would work, if Austrian, like the Steyr Clubman, is OK), substitute aluminum 27" rims for my 26" steels, and you have it.
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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