For my pistons, I chose to use silicon/nickel aluminum, alloy 4032-T6 because of it’s high wear resistance. This material is commonly used for brake master cylinders and forged pistons. I was able to purchase some 26mm diameter material, which worked out just fine for the 1.000″ finished O.D. of the pistons.
For the full floating wrist pins, I started with some 12L14 unhardened precision ground shafting from McMaster-Carr. This shafting, p/n 1327k52, has a diametrical tolerance of +0.0000″ to -0.0002″ with a 10rms surface finish. The aluminum rivets used for the buttons were also purchased from McMaster (p/n 94439A330).