Oddly the O rods have cast pistons OEM and the X rods have forged pistons, not sure if they are OEM or not.
From the looks of the age of the piston, it would have been TRW at that time, before that number went to Speed-Pro. All of the "Lxxxx" numbers were originally TRW. The TRW are block numbers/letters....the Speed-Pro are pinstamped
Back in the 80s managing a salvage yard and playing with circle track racing we discovered that most if not all of the HO 305 engines in 3rd gen Z/28s, Monte Carlo SS cars, etc came with X rods. FWIW