Thanks. I had to go back and re-read your statement about the factory head bolt. I didn't realize that position has a tapered shank so this all makes sense now. You're essentially putting the oiling system capacity back to the stock configuration. Since the stud is a consistent diameter, it eliminates the gap inside the bolt hole that the tapered shank would normally provide. One day I will get myself a milling machine for things like this but there is a shop in my town that could probably do it pretty easily.
But other than indexing the recess towards the oil holes, is there a specific height/depth/length you use for the recess? What size ball end mill is used, looks like maybe 5/16" or so?
Also, some of my studs don't thread all the way down into the block, there's 1-2 threads proud of the deck surface. I called ARP about it and they said it's normal. I checked this on another 340 block and it's the same thing. It shouldn't affect anything though except for the height where the recess starts. I can measure but just asking since you've done it already.