I checked tonight after work on the #3 main as it drilled harder than #4, #2 and the original #1 I had drilled.
I thought something was suspicious. LOL
It basically did the same thing as the 2nd time I drilled #1 up to the other side galley.
I got some safety wire and started fishing around with a small hook on the end to feel the passages.
#2 and #4 felt as they should smooth and then dropping into the oil galley.
#3, had a little hiccup and eventually I was able to get the wire to come out of a top hole in the head.
Bummer.
#1 would have been fine with the set screw at the main saddle and the expansion plugs pushed back in deeper to prevent oil getting into the coolant passages.
#3 I have no way to get back in there.
Maybe this is why some books say to use one size smaller than 5/16 to drill the feeds to the mains.
Amazing the drill did not follow the previous hole.
If I was trying to do that I could have never made it happen.
I do have another LA 360 block I can use.
I wonder if filling this one solid and using a Mac truck oil cooler would work??