don at modular madness has done this conversion before, and says its pretty expensive.
you dont mention what vintage 4.6 dohc and it makes a difference. pre-99 cobras use the dual port heads while the 03/04 cobra intake manifold only fits the tumble port heads.
better off by far getting the fr500 intake and running a novi or procharger on it.
Talk to sullivan performance.
I believe they are working for an intake designed specifically for this application. This intake would also be compatible with the Kenne Bell and Whipple obviously.
I believe this company is still in the development stages of the product but you should give them a shot anyway.
Contact them here: