My original 360 build was with a highly massaged set of those. Trimmed the dome and milled the underside of the dome to the tune of 30 or so grams. Overall, between pistons and rods I took 800 grams out of the rotating assembly. After I blew that up, my new KB forged 12.5's with Eagle h-beam rods were an additional 37 grams lighter per hole. I'm pretty sure that old TRW piston can't be used without a lot of checking and massaging of the dome.