Well it's a model UO8 and the decals in conjunction with the chain guard should place it circa 1974. The rear derailleur is a replacement for the original Simplex Prestige.

Do whatever you have to do to make the bicycle suitable for yourself, It's meant to be ridden. But be aware that French stem are slighty smaller in diameter, so to replace it will require one of the correct diameter, or you can sand down a standard stem to fit.