SCOBRAC's post is correct BUT...... I've never seen one of the "cast as a SO but not drilled" blocks that had the plugs in the
oil passage on the side of the block. The ones that were cast with the provisions but not drilled usually do not have the plugs in the side of the block. It is entirely possible these are not even the original blocks for the boat. I've bought real side oilers out of boats before, but they were not original to the boat. I had 2 hydraulic lifter side oiler blocks that turned out to be the biggest pieces of crap I ever dealt with. Never had a problem with a hydraulic center oiler though. The easiest way to tell is put an allan wrench in one of the plugs and see if
oil runs out. That should clear it up for us all.