ya'll arent doing the exhaust port to header transitions correctly....unless your running custom headers with a 30* upward swept primary....
your exhaust tubing is at a 90* angle to the gasket surface...it doesnt help your airflow much to have a sharp turn.
you want to open up the roof for sure, but more must be removed from the port roof midway between the valve guide and the port exit to help curve the airpath so its a smoother transition.
unless your sure of having no core shift castings to start with it'd probably be smart to have the thickness sonic checked as some of the ****ty heads can be thin at the coolant passage.
unshroud the valves more and clean up the chamber at the casting to machined area's.
if your not sure you can use a variety of cheap picks to scribe your bore onto the head through the spark plug hole to help you keep from removing too much material
