trying to identify aftermarket 340 Pistons

That number doesn't show up in my 80s vintage TRW catalog.
As others have said, sealed power, or badger.
For the new pistons, check out UEM, Keith Black, Icon, Silvolite (all tye same company) One of their lines will have something you like.
Edit: Silvolite are cast, KB are hypereutectic, and Icon is the forged line.