Porting is a art, I'm not that good at explaining things or confident enough to give that advice. As far as my steel sleeve CG alls I did was clean the casting flaws up on the ports & removed any dingle berries that might cause harm. You dont want to change port height until you understand port timings. You could take a 1mm or 2mm off the sides of the ports & not effect port timing. Its said that what ever material you remove from a port, that you should remove the same from the other port. So for example if you take 1mm off the sides of your intake port, that you should try & take 1mm off the sides of your exhaust port.