I have a J150plees. where can I obtain a set of illegal 91 heads? Also, what distinguishing casting marks, or casting numbers, can I use to identify these heads? Lastly, is 91 referring to 91 cc's, the size of the combustion chamber? Will it hurt or harm the cylinder heads if I have them surfaced? I have heard from mercury guys that you can have the heads surfaced and that will bring the compression up due to the fact that you are bringing the combustion chamber further downward. Is there any truth to that?![]()