Blue pill or red pill = 675 or 920

All the work you are planning for the 920s in post #8, is a LOT more than I would put into (almost) any iron head.
675s ready to go, bolt em on and fly it.
(How much horsepower better do you think the 920s will be? 20? 30? Think that will be necessary for a 318? Price the machine work you are contemplating, I'll bet you decide not to.....)