Ok, one last thing here ... just to give you an idea of how awesome this frame is (and I don't think it was ever made in Reynolds 501!) here is the 1986 catalog page:
https://www.bikeboompeugeot.com/Broc...20Page%205.jpg
The Mont Cenis only weight 0.6 pounds more than the PX10, and 0.4 pounds more than the PZ10! It's really, truly a super-light, there's a reason it was around
#3 in the chain for a few years, in a line of a dozen or more road bikes.