Not all PX bikes had Nervex, if I recall correctly. I see a Reynolds 531 sticker, forged dropouts and chrome socks on the fork and stays, so it is a quality bike. Most likely some PX variant, but I am not an expert on these so I'll let someone else tell you more.
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1964 JRJ (Bob Jackson), 1973 Wes Mason, 1974 Raleigh Gran Sport, 1986 Schwinn High Sierra, 2000ish Colian (Colin Laing), 2011 Dick Chafe, 2013 Velo Orange Pass Hunter