I just finished building a motor somewhat like the one your are building, and I would use the second one you posted, the 544, thats what i am running, and it works well , great out of the hole, and good top end, and i have no problem pulling skiers if need be! it is put out by crane, its the enigizer kit, comes with cam, lifters around 135 bucks, but make sure you have at least 135lbs spring presure at the seat, or you will start to float valves at around 4300, my boat is also a 18 ft boat , so weight wise should be around the same.if you want pics email me at boatdawgo@aol.com