That motor sure sounds good. I would guess it's not a stock CC cam in that high revving bad boy. I love the way that boat rides flat at speed, deep-V slicing like a knife.
I've seen some reference to the "high performance" CC motors in the past, and I've seen one with 11.2 compression, which I understand was the 350-hp version.
Personally, a 11.2 350 would be fun, but really a problem for the manufacturer to warrant. That's too much compression to last anywhere as long as the 8.0:1 ratio on the dimunitive 327F with 210-hp. When it comes to that unruly group known as the "general publlic" it's tough to sell and warrant a product you KNOW they'll use. If you have 350 hp you'll be out there using it, ha. Fun? You bet. Long lasting, uhhh, maybe. Fast, most certainly.
The 11.2 = 57cc cylinder head
The 10.3 = 64cc cylinder head
The 9.9 = 69cc cylinder head
The 9.0 = 76cc cylinder head
I understand the 350-hp version was available from CC as the "High Performance" motor, and it was probably a low production product intended to allow the XK to remain competitive with the Donzi or other muscle-boats that were being sold at the time. Along with the higher compression heads, I'm sure a more aggressive cam was also offered. It's a testament to the ability of the hull to take that kind of power, and I suspect it did so with ease.
With your boat having 300-hp, it seems to be PLENTY fast, and not in the "insane" category. In any case I learn something every day, and when it comes to CC marine motors and the Commander family tree, so much the better. Listening to the motor in your video, I was reasonably sure it wasn't the 327F I'm acustomed to hearing, with 8.0:1 compression.
However, I think the problem probably allready solved itself. Most of the 11.2:1 motors have allready burned themselves up. Anything over 9.0:1 requires a special cam designed by someone who knows about overlap, in order to work with the compression and deal with the detonation problem. The worse the gas, the worse the potential problem. In this day and age, high compression is more of a liability unless you have a computer and fuel injection, perhaps variable camshafts.
I don't think the quality of gas is going to get any better during the next 5 to 10 years.
The boat originally had 350/350hp Chris Craft engine in it. It had a big AFB carb on a Wiend high rise manifold, 202 heads, solid lifter 3/4 race cam, pop up 11 to 1 pistons, 4 bolt mains, transistorized ign and the engine was balanced and blue printed.
The Chris Craft mechanic in Seattle said that the engine actually produced closer to 400-425hp, which I believe. It was too much engine for the boat. It would not run on regular gas only on 101 octane, spin the hub on the prop, suck gas big time, need a tuneup and the valves adjusted every other year. In about 1978 the engine broke a rod cap and wiped out the engine. A replacement engine was about $4500 so we went with 350/300hp engine for $3000. It was the best thing we ever did. This engine runs on regular, has hydraulic valves, not as many tuneups and does not suck gas like the old one did but accelerates and goes almost a fast.
This boat was the first 1971 XK19 so I assume they may have tamed down the later boats to be more manageable.