If your 261 was equipped with a FULL FLOW external oil filter, you MUST NOT plug up the holes. This will completely cut off oil flow to the engine....dead engine. This is when you need to route an external line from send to return.
If your 261 is equipped with a PARTIAL FLOW external oil filter, you can simply plug the holes.
Someone will pipe up, and let you know what year the partial/full flow filter change-off happened.
