BRC Performance has a set of domed b20 pistons set up for: 6" Chevy rods, no offset grind, and just .030" overbore. Pistons in 2618 (or their proprietary version of), pins (.927"), rings, and spirolocks (blech), $350 obo

Lot of money, and anything but a combo I recommend, but these are nicely engineered modern pieces. They are not the "picture in time" NOS vintage stuff/crap you see on Ebay, and the price does truly represent a savings, and they are somewhat "soft" on the price. This set up is what B20Paul raved about Brickboard and Turbobricks back a while ago. He actually used vintage Alfa DOHC 4cyl rods, but very very similar dimensions.
Contact me for the email of the employee there who is the one to talk to.