1973 Le Jeune

I think it came out about '83. If it's really a '73 bike it's likely 531. Some of the stickers are hard to read.
Take a look at
www.yellowjersey.org/vintube.html
The top sticker is 531, but easy to misread as 501.

Too bad you need to sell it, but you should get a good price.

They're known for their track bikes. From 1997:

http://www.sheldonbrown.com/vrbn-g-n.html#lejeune

If I were you, I'd list it on eBay or Craigslist. You might get a nibble from a vintage collector. Yours is missing some of its original parts, but the frame itself looks similar to this one:

http://www.classicrendezvous.com/France/bicycles/LeJeune/LeJeune_track.htm

BTW, what's wrong with the saddle? Is it not a Cinelli?

Also, was your frame made by Bernard Carré? (look for name on seat stay cap). If so, that would give it some added appeal to prospective buyers.