If the serial number is not under the bottom bracket as Poguemahone suggests, try the left rear dropout. I seem to recall them being stamped there on the lower models during this era. There should be two groups of numbers. The first group will have four numbers. The second group should have three numberts and is usually stamped at right angles to the first group.

Given the extra component info, I'm tempted to go out on a limb and declare it a 1974 Gran Sport. This model had down tube shifters in 1973 and the foil decals had disappeared in 1975. As Poguemahone states the bicycle was equivalent to Peugeot A08/U08. Hubs with wing nuts were standard, but $5.00 extra got you quick release skewers. The skewers were typically Simplex, but due to the shortages being experienced at the time, other makes were not uncommon.