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Comment: I made the cylinders first, out of 1-1/4" x 1-1/4" x 2" aluminum. The cylinder is 1/8" off center from one face, centered from the other. This allows enough "meat" on one face to drill and tap a pivot hole.
The cylinder is bored 1" diameter to a depth of 1-3/4". This depth allows me to use a 3/4" long piston. (A short piston, for example 1/4", would tend to twist and bind in the cylinder, from the side forces exerted in the conversion from reciprocating to rotary movement.)
I then turned the brass pistons to a sliding fit in the cylinders. The two cylinder bores are "purt near but not plumb" identical, so each piston is turned to fit its cylinder. A builder with a better eye and measuring equipment could make them interchangeable. The pistons are center drilled and tapped 6-32 for the piston rod.
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