You don't have to limit yourself to GT40-based designs. There is a world of possibilities out there for SBF cylinder heads that enable emissions-legal bolt-on installation. Trick Flow, Brodix, World, Edelbrock, etc. all come to mind, and they're all usually about the same price (~ $1000-1200).
As long as we're on the subject, I wouldn't rely on the cylinder head company to equip the heads with the best or most cost-effective valvetrain components. You're better off to obtain your own and set them up yourself, IMHO. I was quite pleased with the results on mine, at least. :thumbup