Did some work on this yesterday. Looking in the stud hole it was easy to see that I did not drill through the water jacket. I looked through the spark plug hole inside the cylinder with a flashlight and I could see some grindings laying on the piston top, not a lot, but there was some. I did compressed air through the plug hole with the shop vac over the exhaust port. When I looked inside the plug hole again, there was no evidence of grindings. Granted, I can't see 100% of the piston surface but I'm going to just assume I got most if not all.
Unfortunately (again) I ran into another issue. Some of the threads took some damage. I cleaned them up with a tap but when I was tightening the exhaust bolt , the stud pulled out before I got to the prescribed 30ft-lbs of torque
So I picked up a Helicoil kit. It'll be the first time I'm using one of those but I watched some vids and it seems pretty straightforward.
I did come up with 1 more question though: since the exhaust manifold studs open up into the coolant passage, what actually provides the seal to prevent leakage? Is it the stud threads? Is it the little "barrel" part of the stud seating into the head? Or is it the exhaust manifold gasket?