Nice score. Archive the Gran Turismo and put on a period correct Japanese derailleur or a Campagnolo Rally (1st gen, 2nd version if you can get one). I use the Rally and i think it shifts well with modern chain/freewheel.
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Flickr Albums
ebay: cicloclassico
70 Pogliaghi ItalCorse, 72 De Rosa, 72 Masi Gran Criterium, 75 Masi Gran Criterium, 77 Melton, 79 Bianchi Super Leggera, 79 Gios Super Record, 81 Picchio Special, 82 Guerciotti Super Record, 82 Colnago Profil CX, 83 Colnago Superissimo, 84 Fuso