I finished the seats by reproducing the slide systems that allow the seat to be adjusted forward and backward according to the size of the pilot.
I used 2 mm brass U-profile ordered in a model railroad shop.
One of the profile is glued with epoxy glue on the underside of the seat and another one on the trunk. The adjustment has to be done with care.
In the photos below, the seats are positioned forward and backward. The fixing in position is done with a scratch glued in place in the middle of the support box and the underside of the seat.