[Water Warrior 2]

Sounds like an interesting project. Just a couple thoughts to add. I am sure there is a bolt or fitting used for checking oil pressure. That could be a source for the oil flow to a cooler as long as the oil pressure is not unduly reduced to the engine. The return line could just feed into a fitting used to replace the oil fill hole plug. Unscrew the fitting when adding oil. Engine can always easily go back to stock and cooler etc can be moved to next bike.
But as earlier said, go with a synthetic oil and don't sweat the small stuff.