I have a similar size boat (1988 F/W H-200), same hull with different top cap (H-200 is the bow rider, Sundowner is the cuddy cabin). Mines got a pre Vortec 4.3 4bbl with a Cobra drive with a 1.68:1 ratio. I’m running a 15x17 alu prop and it performs about the same as yours, perhaps a bit slower...