Derbi metrakit won’t work because the wrist pin is too low. Gila won’t work because the intake is open at BDC. The eurokit would also have this problem, but the holes are smaller.
The stock Zeta piston has no holes and intake side is much wider.
So the hunt is on for a piston that works. Maybe a scooter?
Intake sides of Zeta (Top) and Parma (Bottom)
Zeta (Left) Derbi Airsal Metra (Right)
Gila in a Zeta cylinder at BDC