valve cover openings

hey guys, i just picked up a great set of valve covers, the cast aluminum ones i like


both the covers have bosses cast in them (one for a 710 cap, one for a PCV) so it shouldnt be to hard to open, but what is the correct way?

drill bit?

end mill ?

dremel ?

i figured i would put a PCV on the passenger side and a oil filler and breather on the other side right ?

and what is the correct size?