I’ve been researching the 165 since I read this post. The general consensus seems to be the 165 has a cam similar to a “RV/Truck” cam. From the boats I’ve had in the past, I’m willing to bet that’s the case. They pulled hard in the 3800-4200 range, but started falling flat around 4500.
One thing to remember is marine engines have a mechanical advance distributor, not vacuum. Also, they are void of emissions equipment, no egr, some don’t even have a pcv. Instead of an air cleaner they have a spark arrester. I believe this is why horsepower numbers are north of what automotive numbers are.
On my boat with a Ford 302, it didn’t have a harmonic balancer. The rear engine coupling with it’s elastomer filling served as the balancer.
