Squeaking Sound Coming from 225 /6

I read something about this issue, many years ago on slantsix.org. IIRC, I think there was an issue with the oil pump drive. It usually surfaced when people added HV oil pumps. The extra load on the oil pump would tear up the drive gear somehow. Or maybe it was that the gear was not pinned to the shaft, but pressed-on and it would spin on the shaft.
Or maybe, that's not related at all. It could just be a failed bearing. Do not drive anywhere, or rev up the engine, until you confirm you have oil pressure. Plumb an inexpensive mech oil pressure gauge into the oil pump. You can also remove the valve cover to see if it is getting oil upstairs.