An update - so, I went and picked up the pistons, all new rubber bushings (including the "tube" that houses the lower slider bolt) and the dust boot and seal. The dust boots were marked as made in USA, but the package showed them to be Made in China.
The pistons were more interesting. Both came in Made in Canada boxes. They looked slightly different (looks like either two different castings or suppliers, not sure). One weighs 13oz, one 11oz. The OEM one was 11.25 oz. I spoke with a chassis engineer for one of the major OEM's (has extensive racing experience too) and he said that that the weight of the pistons will not make any difference on the braking forces on the pads. So, no reason to freak out and and swap them out with the vendor - But of course, it adds 2 oz in unsprung weight to that corner.
The metal on both is polished, nice. If you close your eyes, you might feel a couple of tiny metal "burrs". So, I'll polish them just a hair before they go on to make sure they are super smooth.
The calipers themselves were OEM Mazda replacements from a few years ago - so they look fine. Will disassemble, clean, reassemble and report back.