Yes there will always be interest in discussing this type of product, but whether it can translate into actual sales is another story.
One thing to consider more than anything else is.....cost! You also need to look at other Inline markets that do offer a performance aluminum head, such as the Chevy 250/292 engines. This engine group is perhaps the largest(interest-wise)for current racing and performance builds. An aluminum 12 Port head is available that replaces the OEM siamese head(similar to the Straight 8), but at over $2500 just for the head(close to $4000 for the total package), total sales can be counted on both hands, even after being available for nearly 30 years. 2nd is the Small Ford 6 cylinder engine. A really nice aluminum Crossflow style head is available from the Aussie Ford cousin for less than $1000, and a brand new performance casting is also available that is even better flowing than the Aussie head. At $1700 bucks for the new aluminum head complete ready to bolt on, the sales of it are really weak and disappointing for the creater who is struggling to recoup his investment and development costs. Many who have bought the head have ended up flipping them on ebay because they cant afford the rest of the components necessary to complete their builds. Even the Aussie head conversion is rarely done, even though the cost is a smokin' deal. Now we come to the Straight 8 which is much farther down the list as far as size of potential customers compared to the Chevy or Ford inlines, and even fewer is actual enthusiasts that would seriously consider buying one. You have several Bonneville guys(2 or 3) and who else. Not to try to discourage you at all. But aside from the head, you are going to have to consider an application specific intake manifold, headers, valve cover, valve train, these are fine for your $1/4M custom car customers, but as the $$$$'s for the head conversion go up, you will see your target market get even smaller than the 2 or 3 that are possibilities so far. Every one likes to think that new technology will eventually catch up to their favorite engine and give them the long awaited holy grail of heads or custom rods and many other parts common to only the Small Block Chevy and other cookie cutter engines, and many will applaude your effort in trying to. A custom head has been discussed here many times before, and would be well recieved if you can pull it off for the right price. Good luck with it and keep us posted.
As far as software, I use Inventor and Solidworks for 3D modeling and FeatureCam for my CAM software, but if you don't already have working knowledge of them they have a really, really steep learning curve.