I think it also depends on the aluminum they use.

This is the block I like

https://www.theengineshop.com/produc...num-block.html

what they say: MATERIAL: 357-T6 aluminum (strongest available

I personally would not use aluminum blocks. I dont see the benefit in a boat. Not as strong, not as corrosion resistant, cost a bunch more......Sure they are lighter, but I dont think you will see a big gain by shaving off 100lbs per engine. A dart Big M iron block, weights around 250lbs. A big M ALUMINUM block, weights about 140lbs.

A big M ALUMINUM block, has a cylinder wall thickness of .140 at 4.600. The iron version, .325 at 4.600.

Id take the strength, durability, and lower cost of the iron block all day over the aluminum block in offshore use. Drag car, maybe not.

The extra 3-4 thousand per block, I would put towards things like Billet caps, 55mm cam tunnel, 903 lifters, shaft rocker systems, maybe little better rotating components, and so on. JMO.

ok fine...
Loose the beer belly and loose 20 pounds that is the next strategy

I'd think that having similar materials with the block and heads be it CI or AL would be beneficial over mixing them, in theory, and losing weight is always a good thing. But then I read that losing too much weight in the rear can harm handling and that the extra weight of a stereo amplifier ahead of the boat's center of gravity will make it lose all of its top speed. I give up.

But i I say go for it and report back with the findings. 👍