These are the KB quench dome pistons for the open chamber head to try and get quench. I was mocking these up in my old 440 as I know some are in the wrong cylinders here. I used them in my old 440 with open chamber 906 heads to get quench in the open chamber and as John stated they are alot of work getting the combustion chambers right and close to equal. I had to do alot of grinding but in the end it had an average quench about .043 to a worst of .048. Much better and easier to build a flattop piston closed chamber head eng. I used these because money was tight and I used what I had laying around for my old 440. But when I built my 493 from scratch I went with the closed chamber head zero deck (or very close) setup. Ron