Quote Originally Posted by dancinggecko View Post
Do not do that! The clearances will be too small and the valves would probably hit the piston. The recesses in the piston are fairly deep, and the valves protrude several millimeters from the head. I would not recommend putting a protruding valve head on a flush valve motor
That's why I'm curious as to what 4d55 piston tops look like compares to later 4d56. I know my head is a protruding valve head. Because I could see that before install. What I do not know for sure is that the block was fro protruding valve head. Because I have not seen piston tops of either to verify.

I suspect that, with 600 miles on it, I am not running mismatched head and block. But would like to see piston pics to satisfy my curiosity...