Just bought these pistons TRW stamped on the inside and 3963550 on the Dome.Was told their 454 LS6 pistons,True? Also have another set of TRW pistons.The TRW is stamped on top of the dome this time. L2308 stamped on the dome.I was told these are L-88 pistons,True?

GM PN: 3963550 indicate 11.25:1 LS6 Pistons using the 3964291 Closed Chamber 109cc iron rectangular port head. The LS6 did not have Aluminum Heads. I think the Speed Pro ZL2372AF (TRW) is the replacement Piston worth approx $81 ea.

The TRW-L2308 is either a ZL1 or L88 427 piston ID today as “Speed Pro ZL2308AF” worth approx $63 ea. The ZL1 was nearly identical to the production L88 aluminum head version of the 427, but featured an aluminum block. I believe the Compression ratio was around 11.4:1 with a 119cc Semi open chamber head.

Great info,Thanks!!