My understanding is that “on the less” side is safer for the tight toleranced engine(s) than on the “too much side”
I’m assuming you have the engine / trailer level?
You’re not alone; we’re sorta in the same boat: because our ski sits all season on a floating port that is never close to “level,” I’ve been forced to adopt the habit of pretty precisely measuring exactly how much oil I extracted and then I put precisely that amount of new oil back in (I have to approximate the amount that stayed inside the old filter.
This way I’ve been able to pretty much make sure I stay right around the quantity of oil the engine left the factory with (I also have to let everyone who uses the ski know where the “altered” reading mark is, on the “off level” floating port.
If you’re sure it is “over full”, definitely extract enough to put it BETWEEN the “low” and “full” marks.
Best o’ Success!
“Discipline is choosing between what you want NOW and what you want MOST.” - Annon