I just did a redtop rebuild, and was in the same boat. My old pistons weren't great and I needed to rebore anyway.
Importantly, the beams head has a much lower head volume than the previous generations. That's partially how that engine gets its high compression ratio (11.4:1). This means that pistons from the old generations don't work. I found that the hard way after trying to use some Wossner pistons for "all generations" 3SGE, and seeing them hit the head.
I measured a 33.7 cc head volume on the redtop head. The internet tells me the blacktop head is 33 cc -- which means the redtop is probably the same and I spilled a bit of water measuring.
Also, importantly, this means pistons made for the blacktop should be ok
(and a nice bump up in compression ratio / power). I don't know if the stock ECU will handle the increased CR.
I used these JE 12.5:1 pistons
for the BT. That solves the ring problem too, because aftermarket pistons come with non-discontinued rings. They fit ok and turn over no problem. Just started that engine for the first time this weekend and went through the break-in. Will circle back here later once I've put a few more track hours on it.
The only thing to keep in mind is the oil squirters. The redtop and blacktop ones are slightly different and the RT ones don't clear. BT ones are easy to find.
Anyway, hope that helps.