that is a pressurized oil passage. I think if you just grind the area without welding there is going to be a small void, and it will be asking for lower oil pressure and a rear main seal leak. a skilled welder could weld it. why guess at plug size? can someone please measure the hole? I do not have a block handy
Ah yes. It didn't occur to me until I thought about it, but you're right. That is the pressure side coming out of the pump (after passing through the cap). A hole there is the last thing I want, looks like it's off to the weld shop we go.