We might not be talking about the same thing, being a danger.
I don't see a lot of drilling in the block.
I only see long hole drilling in the manifold piece. All other drilling is small holes.
I don't see how the block can "go bad very quickly".
Please help me understand.

I am, and many above, are referring to drilling the block for pushrod oiling in the manner the OP discussed, as Indy or KB would when they manufacture the block with the pushrod oiling option.

I'm not talking about the machining required for adding the manifold and oil supply lines to the lifter valley.

OK, now I understand.
I also agree, drilling galleys in the block, very bad.
Thank you.

I think that is good advice for any backyard guy but based on what I know about Indy, I doubt that they have any sort of "sophisticated" process for drilling these holes. I'm pretty sure I could come up with a method for drilling the holes that would work as well as anything Indy has. If someone who has toured the Indy machine shop wants to weigh in with a description of the Indy "hi tech" process I'm all ears.

Deep or long hole drilling success is as much related to the drill edge profile and drilling technique as it is the machine the block is being drilled in. The guy running the machine is going to make the biggest difference.