. At an earlier time, like the middle '60s, Thompson Products made PowerForged pistons that were marketed as aftermarket replacement pistons. I used them in the first y-block I rebuilt in 1966.
Thompson Products merged OR became TRW at some point in time. You might be able to determine the history on this company change using the Internet.
TRW continued to market replacement PowerForged pistons. You know more about what became of TRW than I do!
Per an old TRW sheet I have, L-2018 pistons are PowerForged and 3.800 inch diameter. I don't know what the 'F' suffix you identified means regarding their oversize dimension for the 3.800 basic bore diameter.
Cliff is correct about 292 y-block pistons having a different skirt configuration than 312 y-block pistons. As Cliff indicated, 312 pistons can be used with a 292 crank, but 292 pistons can not be used with a 312 crank due to an interference issue.
Forum Moderator John 'Hoosier Hurricane' in a posting some years ago explained what modifications he had done to utilize a set of GMC C***Y pistons in a y-block he built. My recollection is that John indicated that the C***Y pistons he used had press fit piston pins where the y-block used full floating piston pins. As Cliff indicated, the pistons John used may have been cast rather than forged. Also, didn't the C***Y pistons have valve notches in their flat tops? John may be able to recount all that he related previously. It almost seems like there was a piston pin compression height issue that required John to machine the piston tops, too.
I suspect that the Forum link with Hoosier Hurricane's posting is so old that the software package changes webmaster Jim Culver has installed for the Forum website would make it unreachable in the archive. John or Ted may be able to answer that accessibility issue.
Silent Rick, I've got a friend with a stash of old y-block parts and NORS parts. Last I knew, he had some flat top replacement Thompson Products or TRW forged pistons. What PowerForged replacement diameter pistons are you seeking?
IF you're going to use a supercharger and are looking to use a static compression ratio of 8.0 or 8.5:1, it seems like you are looking for a set of y-block 5750 / 471 cylinder heads. Rono is someone you should try to connect with on this Forum. I recall that he's using a set of 471 heads on his supercharged engine. I think he's using the same intake manifold you're talking about using as well.
Hope some of this helps!
a.k.a. Charlie Brown
near Syracuse, New York