The 4-cylinder air-cooled Continental A-65 is about as simple an aircraft engine has you can get. However, the procedure for changing the oil in it is a *bit* – but only a tiny bit – more complex than that for your small-block Chevys and the like. Kevin Lacey, of Airplane Repo fame, does an excellent job of walking through the procedure in the video here that shows him performing the procedure on his Taylorcraft’s power plant.
As an aside, he also walks through the procedure of cleaning spark plugs and testing compression since the engine only had 23 hrs SMOH when the video was filmed. Those’re helpful to know as well.