I just bought a 2004 Larson 17.5' bowrider. It has a Mercruiser 4.3 LIter, Serial number 0M693427, with Thunderbolt V Ignition. Drive is Alpha One, Gen II (I think, sticker label is pretty rubbed), serial number 0M491238. This boat needs a new prop. I guess I need to know the horsepower to...