What I am going to do, and what warmonger did:
1) Remove the cams and replace the valve covers - this shuts all thew valves.
2) Plug each port firmly with a rag, down far enough to give you enough acces to where you need to grind without touching the rag.
3) Then smear vasoline or grease around the port to catch the filings.
4) Grind
5) INVERT the motor
6) wipe up the grease/filings goop
7) shop-vac the other filings
8) remove the rags
9) shop vac more
10) Turn the motor the right way up again.
