If you have the oil pan and off you can look in the oil hole and see if the passage is open or not. for full flow oil filtering you must block the vertical passage between the two large oil ports.
If you need to remove the dowel pin I would drill and tap it 1/4-20, apply some heat around the area and use a slide hammer to coax it out. Instead of driving an old pin in to block the flow it is probably safer to remove and use a new pin (if necessary) and some sealer.
Grigg
