Use the 3/4" plug to take out the oil
Use the 3/4" plug on the starboard side of the engine at the top of the crank case and below the carburator. That's what it is for. Use a simple hand pump with plastic hoses. Yes it can be a bit messy but not if your careful. Can't imagine waiting to take out three-four quarts of oil through the dipstick!
Early engines had a built in pump that stayed screwed into this access point.
Buy the Moyer Marine repair manual. It shows how to do many maintenance procedures.