While were looking at this side of the motor the oil pan will block off the oil return if you have an oil pan gasket lay it up there and you will see the oil return for the time tunnel is blocked off.
Yes the oil pan will cover most of the original hole that was there that's why there is more of a slot there now. I have also drilled and tapped 4 1/2NPT holes right under the cam next to the back of the mains for oil drain back. I know if gets into the swinging assembly it will cost HP but for now getting the oil back to the pan is more important than windage loss.
