They are .060 - 12.5 with 78cc heads. You can use a cam with about .550 lift with no fly cutting with big valves. They make compression but keep an eye on the extended spark plugs! They are for a 383. I have used them since the 70`s and they are a old design. If you decide to not use them, hollar at me.
Those are 383 pistons which have 1/16,1/16,3,16 ring grooves. They are 12.5-1 with a 78cc head. Old school,heavy,powerforged pistons. I run them with a full floating pin,non-bushed. If you want to run a more modern designed,lighter choice,let me know. I'll buy 'em from ya. John