I'd start with...
3D CAD
Billet Aluminum (not enough volume for castings)
5 axis CNC
DOHC
Modern chambers NOT necessarily Hemi
3.62 or shorter Stroke
Zero deck
Belt Drive cams
Off the shelf rockers
Crank trigger
Dry intake EFI
External oil pump
I will begin by posting this, I am NOT trying to discourage anyone, just make them aware of the facts. Don't expect to have people beating down Your door, You will have to
commit to doing this with the mindset it won't make You a dime, that is all. I have been working out ideas that will accommodate stock manifolding, and provide even an
otherwise stock engine with improvements, & of course the ability to really honk for those who are going for it. Trust Me, I've thought of a 4 valve arrangement, even
using a stock type cam in the head. But this narrows a very small market down to a teensey weensey one, nobody (say eddy/weiand/etc.) is going to make a run of
these. Billet? Been done already, & with that I will leave You w/this link........ Slant Six Forum, :: View topic - Aftermarket Aluminum Cylinder Head?