Get a grinding stone to do the cutting and use a cartridge roll to finish it off. Whatever you do, make sure not to make the port into a "bell" shape at the end of the port, make sure to go back at least an inch or more. Also the straighter the better so if you're gonna re-shape the ports, take more off the short side because that is where the most airflow will be found. Good Luck.
P.S. I've been drinking tonight so if none of this makes sense then please disreguard
