Parts got here in less than a week !
I asked a fellow engineer some feedback about the piston and cylinder with the old japanese part in hand and the opinion was the parts look OK.
Cylinder is sand casted so should be better as far as heat dissipation is concerned.
He pointed out some areas that needed work on the piston wich I did.
I then polished the piston crown (work is still in progress).
Valve cutouts were there from casting and the piston top had been flatted in a lathe as there was circular markings wich got away.
The piston alloy is quite tought compared to some other alloy stuff I have been polishing (SU carb for instance) so I quite feel reassured.
Hers is a view of the polished chamber too :
You might have notice the quench / squish area had a hard time pinging, it does point out the cooling must be improved if I want to run decent CR.