Magnum Heads

I would say that you can't do it that way. The vertical holes have clearance chamfers and a drill would walk making for an innaccurate hole. I believe it's the moparstyle forum where some one made a drill jig that they lend out so you can do it youeself or it will need to be done at a machine shop.

Don't knwo anything about 308's, I was always under the belief that all 360's up to the magnum introduction had open chamber heads that essentinally had the same port design as every other 340/360 head.