I have those pistons in my 440. I did not use clay to check valve clearance because a friend ran nearly the same combo with no problems. I realize that all engines are different and I should have done it anyway. I have the .650 lift Comp cam. The heads are ported 906s with 2.140 intake and 1.880 exhaust valves. The block has also been decked .060. The pistons have not been clearanced in any way. It sounds as if I have been very lucky to have not had any clearance issues.