The Zlin Z42 is the classical example of a rectangular wing with near to elliptic lift distribution. The benefit is to have only one sort of rib, instead for each section at different rib.

I would not take F18 as an example. Since the foil (and hull shape) is the only "unlimited" part of the boat, builder try to differentiate here, well I think that's why you put the quotes around it). At the end they have very different daggerboard and rudder length, so induced drag is not as good as one may think. I guess that shapewise A-cat (before c foils) is a better example.

Actually I think the foil looks like a section of a Mach 2 fighter aircraft from the sixties and hence totally unsuitable for a boat. They are very thin and pointy at the nose and this causes the early cavitation. I guess in the beginning without spi and single trapez it was fine, but once the boats got faster... My friend had an old (30y, Panthercraft I think) T. Later he bought some of this wood core rudders. Very beautiful, but as thin as the old once. So I didn't see evolution in the rudders.

I think I would ask a carpenter with a CNC machine to cut me the wooden core and laminate glass or carbon around it and sand and sand and sand... I don't have the talent to cut and carve it or cut and fill it (as in your link) by myself.
Other possibility, ask the carpenter to cut a female mold or cut your female mold from wax or foam with the hot wire method (not sure if it works for high aspect ratio). Or take an existing one and take a negative of it...
I don't like the female mold method because it is difficult to get a reasonable core or framework in the rudder. That's the reason why so many boards are heavy like stone, overcame the core weakness with extra skin thickness. If you have a wooden core you can go with glass and you are still lighter than many carbon boards.

From a structural point of view the ultimative boards are extruded aluminium: Topcat
You may ask the dealer for a price.

Cheers,

Klaus