I would have YOUR engine rebuilt by a reputable Buick V-6 engine builder from here on the board. Too many "rebuilders" think every engine is a Chevy, and can be built as such
You wont get turbo pistons, they will be cast. I took an engine in on trad that was a brand new reman just too see what it was and guess what, no turbo crank, no forged pistons.
Why would you expect forged pistons in a reman from an auto parts store? They came from the factory with cast, not forged. Different from NA, but cast.
I bought a surefire engine from autozone two years ago to go in a gn I once had......it has been at twenty psi on a regular basis....still goin strong....im adding a trans and a turbo for the guy right now...