It's likely a different cam than Ford put in 351 truck engines in the 80s as trucks had emissions requirements whereas boats didn't. So it's quite possible the cam is a bit different and may have made a bit more power. Hard to tell since boat HP was rated at the crank and car/truck HP at the rear wheels after driveline and accessory losses.

I'd be surprised if the PCM 351 cam was at all aggressive with lift or ramp rates and I'm with a 4400 RPM max it's not going to have a lot of duration or overlap. What we'd want for a mild performance build ina towboat is more lift and faster ramp rates along with slightly more duration and overlap. Nothing excessive since we want a broad torque curve for wake sports. Slalom and barefooting you can build for higher RPM.

Also I doubt that PCM cam in either 351 or 454 is split duration. Not sure on BBC but all Ford engines benefit from longer exhaust duration due to restrictive exhaust ports as cast. BBC has pretty decent exhaust ports relative to Fords but I'm sure more exhaust duration would help BBC as well.