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You are correct TT, all Lotus Ford derived engines are twin overhead camshaft & as such I would have been a bit useless for marine purposes. Cosworth did produce an ally head, but even in the day they were very rare & expensive, so again I doubt if anyone would use one for marine use, unless they had a cossy engine left from a terminal racing accident!
Although I suspect this thread is now dead Aquaplane made an aluminium cylinder head for the pre crossflow. I remember Mangoletsi for inlet manifolds but it seems they also did marinisation kits, one of them uses a pipe through the sump of the pre crossflow engine as a heat exchanger.
I think Cosworth did do an 8 valve conversion on the 1.5 for Lotus. It was fitted to the Super Seven. These cars known as Super Seven Cosworths had a nasty habit of breaking rear A frames as the Standard 8 axle tried to cope and twisted under torque.
I have swallowed the anchor but have not tried mud weight yet!