I am busy preparing my barrels before plating and threw a dummy assembly I
found on both cylinders that on the one side the piston is level with the intake
port and on the other side the piston is about 0.5mm over the port.

Any advice on fixing this problem? This is never been worked on barrels
and tops. I'm asking this because there is so much that has to be looked
at when skimming a barrel.