If I was wanting a 428 engine in my original Cobra I'd be looking real hard at the rest of the car as well.
It would be rather foolish, I think, to become so focused on the correct engine when other original specs aren't even in the ball park. Going 428? Get the rest of the car up to speed with that goal as well. OR, slap some side pipes on that street car, drop in the 427 and be happy!
