My thought is it's likely make a very nice fixed gear if much of it needs to be replaced. If it's a seventies model, it likely has very limited braze ons.

However, are you saying the headset and bottom bracket are shot as well? On older gitanes, these would be French threaded, and replacing them will require an investment of time or money. It can be done relatively cheap, but require some patience to hunt down the parts. If these parts are intact, I'd say fix it up as well, a fixie.

Personally, I find restoring (okay,rebuilding) old bikes a fun diversion, so I'm the wrong person to ask.