HI, id just wanna say awesome work. I got inspired from this.
I had plans to make something similar, But split the "gearbox" in 2 pieces. Main piece would be the Shiftstick and the thicker rod with the grooves. that could be sturdy and easy adjustable. The bottompart that is the gearchooser could be in a box that is tucked away in th rig and connected with a thinner rod with a sturdy linkage instead.
But... once again .. awesome work.. im impressed!
(sorry about the English, im from sweden and i know no french i just google translate your side.. google needs to learn french though xD )