Scaled down and simplified construction. Almost everything is press fit and removed the need for bearings. I'll include thicker valves incase the original is too thin but then you'd have to drill out the top and valve tops. This is still a wip as the cam gears need teeth.

You'll need 2x M2x6 screws for the piston rod and cut pen springs or 4mm x 10 springs for the valves.