I always clean up the ports Intake/Exhaust and open them up, to match my set up. Set the gaskets on the studs, take a marker and trace the inside of the gasket onto the cylinder. Remove material where it is shaded in. Make a happy transition from tracing, to existing portal opening. And Don't go into the cylinder port opening window!
This is really kinda why you want to match the case, right? Flow! From intake, to case, to exhaust! A Happy motor it will be. When it is all done, it will be worth it. Brent