The cylinder was machined before the piston so the latter could be made to suit.
The cylinder bore needed to be parallel and round throughout and the diameter correct enough to suit the O-ring included in the kit.
To start the cylinder was clamped in the 4 jaw chuck, checked to be square in both axis using a right angle edge against the lathe bed.
In this setting the port face of the cylinder was machined taking the cylinder height down to the correct overall measurement and giving a datum face for further operations.
Next, the cylinder was clamped on an angle plate against the faceplate and set to run true as shown using the outer edge of the cylinder as a datum.
In this setting, half the amount to be removed from the cylinder length was machined from the end face.