Finished the work, finally
It was funny when dad sat into it, got cozy and said: "Hey, this is like the real thing!"
Plans:
Get rid of that ceiling "thingy"
Weld some sheets between the ceiling and collcage
add reinforcements to the rollcage
make a better footrest for the driver
make a footrest for the passanger/co-driver

bleed the hydraulic handbrake
paint the pedal "legs" black
lose mechanisms from the doors
use lexan instead of glass for door windows
a tray for the battery in the rear of the car
[...]
Paint the whole interior white, including door posts and ceiling this time =I