Is there a decal, most likely on the seat tube, stating what type of steel was used? The PLX8 was made from Peugeot Helium tubes while the PLX10 was made from Vitus tubes.

As far as the serial numbers, Peugeot used a 5 digit number for bikes manufactured in the '50s, a 6 digit number for bikes manufactured in the '60s and 7 digit number for bikes manufactured in the '70s. In most cases, the first digit in the serial number was th year of manufacture. In example, a serial number of 123456 would indicate that the bike was manufactured in 1961 and 1234567 would be 1971.

Her are a several good Peugeot web sits to visit:

http://retropeugeot.com/

http://www.cyclespeugeot.com/index.html

Hope this helps,

Gary