The decals and serial number are consistent with 1977. I believe the PX-10 still had chrome stays at that point, although that feature disappeared over the next few years. The 25.8mm seat post diameter, presumably with a 28.0mm seat tube outer diameter, would be consistent with straight-gauge Reynolds 531 tubing (or Reynolds 501????), but the PA-10 had straight gauge carbon steel and the
PR/PK-10 series had the same double-butted main triangle as the PX series and should take a 26.4 or 26.6mm seat post.
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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