1972 Demon with 71 340 casting

1971 CY Dodge Dart said
My 340 was built using these pistons.
Sealed Power 428P30 Sealed Power Cast Pistons | Summit Racing
I guess it's safe to assume it doesn't have the stock 10.5:1 compression form the factory anymore.

No sir, I don't think it does. Those appear to be the late 73 and 73 pistons. But that's not necessarily a bad thing.