Let us know what you find. You said it looks like it's coming from high up on the back of the block, I was gonna say leaky sender, but that's a LOT of oil.
I had been fighting what I thought was a leaking rear main seal. I finally pulled that motor to install my stroker and it turned out to be the soft plug that’s behind the cam. The plug is in excellent shape but it’s not something that I’ve never seen before.