For my own edification and to clear up any confusion, here are some pics comparing a stock head bolt to an ARP head stud. OMM used the word 'taper' to describe this situation but I would say it's more of a step. Normally I'd think of a taper being like the conical area underneath the wider part. Either way, you get the idea.
Here's the stock bolt. Note the step in the shank under the head. I admit I had never noticed that before. I always knew the one bolt was a different length but never noticed the step or what it might be there for.
View attachment 1716168050
Top of the shank diameter measurement.
View attachment 1716168049
Diamter decreases .050" below the step.
View attachment 1716168048
ARP head stud shank diameter. There is no step as with the OE bolt.
View attachment 1716168046
Diamater of the bolt hole in a stock, '70's cast iron cylinder head.
View attachment 1716168047
Diamater of the same bolt hole on an Edelbrock aluminum head.
View attachment 1716168045
Even though the step is clear as day now, I'm still not understanding the point of it and it's affect on oiling. There are two holes off the rocker stand oil passageway on the intake side of the hole; one is above the other by about 3/8" or so. In my mind, pressurized oil comes out the bottom hole, fills the area around the bottom of the bolt shank, goes back into the top hole and then out the rocker stand orifice. Again, my best guess for doing this is that the oil flowing around that bolt shank creates a dampneing or swiriling affect on the pressure feed so it does not just spray everywhere.
Regardless, since the bolt holes in both the stock and aftermakret heads look to be about .0025" larger than the ARP stud shank, some amount of oil is definitely flowing around the stud shank. Machining a recess in the shank will obviously add more volume but again, it does not seem necessary since there is no step in the stud like with the bolt. Without that step down in diamater, the airspace volume around the stud shank would probably end up being about the same as with the stock bolt. There's no need for the step anyway because there is no bolt head.
So yeah, I'm just gonna stay with the studs as-is. Never been a problem before and now that I verified things with hard numbers, I really can't see how a straight-shank stud could create any sort of restriction since the inner diamater of that bolt hole provides enough volume for that little bit of oil to flow into.