You have 2 very costly options, or you could just fabricate a spacer and use a Holley 500 carburetor. If that's fuel injected rather than nitrous-injected, then Holley makes a 670-CFM 2-barrel TB you may wish to adapt.
The more costly options are either sending that one to Extrude-Hone, or a fabricated sheetmetal manifold.
That one you have shouldn't be too bad if you add a Chinese turbo to pressurize it.
The length of the runners will affect the RPM range of your powerband even more than your cam specs, so if you want more RPM, then you'll need to go with a custom fabricated design with much shorter runners and a much larger plenum.