Thank you for the info and comment Pierre Louis, I have now a low-cost solution to give to my GT40 a more historic appearance !
Important step last weeck : I made the first track test .....
The track was Le Luc , a small but interesting 2.2 km track in South France , ( 50 km from the well known Paul Ricard ...) .
I made 35 laps ( 4/5 laps cessions...) at reasonnable speed , max RPM set at 4500 ...
The feed back is very encouraging : only minor problems ( self openning driver door... and minor oil leak on oil tank ..) and a good car behaviour in the main areas :
Stability in the straight portions, front axle directivity, brakes efficiency , no sensible bumpsteer ( but the track is in good flatness conditions ....).
Gear box ( G50) and clutch ( 911/965 turbo ) where OK ...
The tires are Falken FK 453 , 225 wide in front, 275 for rear: not slicks performance level of course, but they "made the job" ...
After "debriefing", it appears that the rear axle is not presently at the level of the front with some lack of progressivity and balance when reaching the limit ...
No work was made yet on the rear set up, so I anticipate to have to work on all the parameters : Schocks , springs, sway-bar, camber , toe, caster etc ....
I don't know yet which to adress first , and of course any advice will be appreciated !