They are what are referred to as forged replacement and are a premium replacement part for rebuilders. These particular ones are direct replacment for 71 six pack engines. By direct replacement we mean can be used without rebalance as they weigh the same as production factory pistons. They feature the standard pin offset as well so I install all mine reversed. They are NHRA legal sub for 71 six pack Stock eliminator motor. BTW
When i built the first OR combo motor it cost $1680.00 carbS to oil pan. Yes I did everything including all machine work and carbs tuning etc but that is still a very imexpensive motor. It ran in my car 9 years of bracket racing. The car weighed 4150 with my nephew driving (200 lbs) and 4256 with me driving (306 lbs). At 4150 it ran 11.49 at 119.11. Even big ol me ran a 11.51 at high 118s mph. I built it in 1990. Motor is still running now in a mud race truck . I have trailered more than once $$$$$$$$$$$$ stroker 451s with all the tricky stuff and have seen it occasinallly run down some engines approaching $20000 in cost. So one can worry for no good reason about the piston wieghts and rod weights and even call it old technology but when it pops the big guns on the trailer and does it virtually mainentance free for 10 to 15 years it is real hard to get too worried about piston weights which are the same as i said as stock. I have also built it with the KB hpyers just for fun for customers but in reality you will NEVER EVER see a broken L2355F piston. They are tougher then tough.
Don

PS HI from beautiful downtown Ameliasburgh