One way to have it done is to wipe a little dykum in between the cylinders, lay up a head gasket, with bolts and washers to position and secure the gasket to the head, center punch where the holes need to be located, then find a machine shop that still has the air table/valve head reconditioner (I wish I know what it is really called but it is ancient technology for doing valve jobs), where the air table can be positioned at the correct angle for drilling. Let me look for a couple of photos I think I have of the head I did this past summer and the drilling of the holes. Not fancy but got the job done.
My young machinist doing his thing on one of my heads!
