the hole is where the aftermarket oil feed line runs from the back of the head to the port typically where the oil prssure piping go's into the block
I'm confused because elsewhere you said...
except for a small hole in a rear oil galley
Can you post a picture of the damaged hole?
The oil galley plugs and the pressure switch hole should be tapped either 1/8 NPT or 1/8 BSPT. If one of those holes are without threads I think you would have to tap it oversized to accept a pipe plug or a bushing. The next pipe size would be 1/4". You could carefully drill and tap the block to accept a 1/4 to 1/8 bushing but you would need to be careful not to run the bushing so deep that it obstructs the horizontal run of the galley.
Doug L.
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