This is what Stephan from Gitane USA says:

Your frame is probably a 1984 European model. In 1984 Gitane switched to the "fast back" seat stay attachment.
In 1984 Gitanes made for the US market used Columbus (Team Pro), the 3 lower priced models had Super Vitus 983 tubing.

In 1985 the US Gitane Professional changed to Reynolds Competition tubing and long point lugs. They also had later style Reynolds decals.
Reynolds 21-24 tubing had a wall thickness of 0.8mm at the butted ends and 0.5mm in the middle. This was some light weight tubing. The down tube may have been heavier gage 20-23 - 0.9mm x 0.6mm.

I would use th 1984 decals on this frame.