Good info here.
I like Bent Ramrod's post.
I would add, when paying a gunsmith a lot per hole, some of that cost of getting it right is he will likely use his mill to set up and drill precise holes and that takes some time to set up.
Faster is to just eyeball the top center and punch the spot that looks good. There are all kinds of "gunsmiths" out there. Choose your smith well by asking question about how he will do it.
For us shade tree gunsmiths, I would add:
Use a drill press and start with a center drill AFTER you are damn happy with your lay-out (all holes) are punched. Check it twice and then check it again.
Use the quill stop on the drill press.
Did I mention, the start the hole with the correct center drill? That will keep the small drill from wandering off to parts unknown.
If you can retain the set-up, go ahead and tap each hole as you go using the drill press to hold the tap center over the hole.
Go slow and feel everything as you do it.
Last, and this was touched on in an earlier post. Go to the rehearsal. Try this out a few times on scrap. Get it right. You will be happy you did.