If the chrome has pitted on the pistons you are best replacing them. Cheap replacement pistons are gold zinc irridited, or black zinc plated and it wears off leaving bare mild steel, so they rust far quicker than the OE chrome plated ones. For really long life you need stainless steel pistons. I can supply seal kits, stainless pistons, stainless pad pins and the special square shaped seals that go between the caliper halves when you split them to hone the bores. These square seals should NOT be reused! Toyota do not list them. I can supply stainless pistons for UK and Jap spec calipers, as well as for most any caliper off any car that I can have a sample piston for.
If you bead blast do NOT allow blasting medium down the caliper half bolt threads. If even a tiny bit remains it will often lock the bolts up on reassembly, and the bolts are a very odd thread / grip length and not available. I can Helicoil mangled ones on a jig on the Bridgeport, and fit a slightly bigger diameter cap head bolts, but it's far better and cheaper not to bugger them up in the first place