I don't see why it needs to be OHC or whipple.

OHC increases cost, weight and size. Whipple is a low volume producer. Eaton on the other hand can handle volume.

There is already a 5.5 L engine in use in C6.R, that will probably be the basis for the next gen.

There is an image of the thing floating around somewhere.

Current guesses are that it either has injectors under the valve covers (direct injection) or some fancy third valve.