Pushrod clearance problems

Guys,

i have a set of eddie performer RPM heads on my 383. the hole in the castings that the pushrods go thru is pretty small. when cycling the engine by hand the push rods (5/16 ) come very very close to the side wall of the holes. i was hoping to run a nice strong 3/8 pushrod but that is out of the question. is this just a matter of taking the heads off and enlarging the hole? im willing to pull the heads and take them to the machine shop to have this done. I am just worried about doing it and ruining the heads.