Does anyone know of a comprehensive list of cyl. head casting #'s for the GA16DE engine. I am aware of two different heads, but there may be more. My '93 has a 57Y casting #, which can be seen easily, on the pass side front of the head, by the side engine mount. As far as I know, there is a later head ['95 and up?] that is reputed to be worth an additional 5-hp. Has anyone got the low down on this? If I'm going to port my head, I might as well start with the best one.