To All
Yes that is a Factory drilled port that was plugged in direct line with the oil port to the rockers.
Years ago it was a Fast and Cheap fix to alleviate a plugged up INTERNAL oil passage to the rockers.
Simply tee the oil pressure sender port and put a piece of copper line around the back of the block to the center of the head and WALLAH,instant oil to the rockers
Regards ,
