Thanks, here is the before picture of one of my calipers that I rebuilt.
My recommendation to buy new pistons from Rock Auto. They are not too expensive.
Also make sure you buy the assembly lube. Don't try assemble them using brake fluid.
As for pushing out the pistons with air. One will always pop out before the other and now you have loss you back pressure to push out the other.
With the two halves to the caliper apart, install a brake pad on the face of the two pistons and hold it there with a C-clamp. Apply air pressure to the the caliper, then slowly loosen the C-clamp allowing both pistons to move out of there bores at the same time.
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