Many of Gitane's of that vintage will have lost their paint by now. I bought a Gitane Interclub in 1972, and by 1975 had repainted it myself - stupid high school tricks (probably would have been better off leaving it though!). Back in those times, the Gran Sport was their basic consumer model, the Interclub was basically the same thing in more of a racing geometry and sew-up tires. The Tour de France was their slightly higher end model with Reynolds 531 tubing, Stronglight crank, etc. The Gran Sport had painted fork ends, my Interclub had chrome forks (halfway down, it was popular then), and the TDF had chrome rear stays and dropouts.

These were all steel bikes, not necessarily all that heavy. The Gran Sport was advertised at the time as being 26 pounds, which is not bad in my (old) book. The TDF was probably a few pounds lighter.

Read Sheldon Brown's articles on french bikes of that era. You will run into french threaded BB's and forks, which will be more difficult (i.e. expensive) to deal with these days. You may get the same bang for less buck with a Raleigh or Japanese bike of the same vintage.

I still have my Interclub, in frame only. I plan on doing what you have in mind.

Good luck!