for whatever reason, the "fineness" of the fins on these cast heads appears to be limited (e.g instead of 8 fins, could they cast 10 fins in the same distance?). Now, they need to be thick enough to survive and to carry heat their full length, and sufficient air must move through the slot between them. But, given that, more fins per inch = more surface area for heat exchange = cooler heads. Can we get better fins if we extrude or cut them? Cost?
Re: finning, the common aero comparison is between traditional Lycoming cylinders (larger, fewer fins ) being designed to "withstand" heat, vs Continental being designed to "shed" heat. Also, based on fin theory, there are a range of options and a specific cross section. "more/thinner" is not necessarily better, at some point.
The Porshe heads machined from solid aluminum block ("Billet" is a sales word that annoys most machinists - a billet is the rolled blank you sometimes see on a flat bed, headed somewhere to be divided down and rolled or cut to small blanks) seem to work? So one avenue for design exploration. Nonetheless, casting is more likely to approach optimum fin shape (cross section).
I'm going to beat on is some more:
Casting, per se, is not the inhibiting cost factor in most cases. If it is, with complete designs and a stated volume (# of parts), it is easy to compare with a "cnc"'d analogue. A foundry will quote per part, based on volume, that appoaches the retail raw metal cost. They of course have to remove the mould & cores from the casting, cut off the sprues and risers, and lightly de-flash/deburr. ("snag" the castings). For a complex item, about 1/2 the metal poured becomes your casting, the rest (risers, pouring basins, sprues, runners) goes back in the pot. A foundry does need enough volume to amortize the rigging they design, develop, and apply to your pattern to make it pourable; + perhaps a few test pours to prove it. This is what makes only one, or only a"few" castings so expensive.
The real, big, costs of getting a part out of the wishing stage is 1.) thorough design and engineering. 2. tooling.