Do one hole at a time. Thread the holes for 1/4" pipe plugs; after removing the plug that's in there, stuff a piece of rag or paper towel in to keep the chips from going anywhere. After tapping, use a magnet & low air pressure (not at the same time) to remove the chips. Remove whatever you used to plug the hole, then use a distributor shaft to create
oil pressure, and let the
oil flush out each hole. Be sure to stand directly behind the hole when flushing so that you don't get
oil all over your garage.
Be aware that the lower hole has a connecting hole not very far in that delivers oil to the rear main. You'll have to be extra careful here to make sure you get all the chips out and they don't fall into the hole to the rear main.