Those pics are Bill’s.  But to answer your question, it’s not a 360°groove unless the cutting tool is worked around the bore in a circular motion.  As long as pressure on the tool is only applied to the crankshaft side of the cam bore, only the three holes will be interconnected, and no groove will be present on the valley side of the cam bore.

Lorena, Texas (South of Waco)

Hello   the groove extends a little past the oil gallery holes that  move oil to head. I put upward pressure  ( toward  crank shaft saddle ) on all tread  to make groove. I might be a little deeper than .020/.030, as I had no way to measure it. Thanks Ted for putting up pics.  Bill Oregon

For those of you who emailed me about the cam bore grooving tool I am using, here are some pictures.
 

 

 

 

Lorena, Texas (South of Waco)

So the all-thread and two lock nuts spin against the two flat washers with just a little clearance?

That’s correct. Just enough clearance to allow the spindle to turn freely.

Lorena, Texas (South of Waco)