I always thought that oil capacities in boats were theoretical, and the actual full mark on a dipstick was related to the engine's level. and some could take more if the engine is at a further down angle than another.
and that there is a plug on the block to find the true oil level when the engine is sitting in the hull in the water.
I always ran 3 gallons (12 quarts ) including filter in that # in mine and never had an issue . The 4 LHA & STP are good bullet proof engines imo .
I think you have to separate out your two points there. The dip stick mark will most likely need to be customized based on the sitting angle of the motor, but that does not change the quantity of oil required- just your accurate measurement of it.