Please note that the prop shafts run on lubricated ball bearings. These are flanged, Conrad type, angular contact bearings made by Barden. They will be operating nowhere near their DN rating. If they fail, they will be replaced with router ball bearings. The cog belts and drive pulleys are the the same equipment that drives 6 lb. buggies at 60 MPH across parking lots and race tracks. The engine to prop shaft ratio is 6 to 5; 6 engine revolutions produce 5 prop revolutions. It is more fun to try this than it is to scrap the idea and put in two mundane .25s.