[Unobtainium]

I agree it should be a zippier motor to stay with the original concept.
It's not easy or cheap to do though. It has to have close to the same power, more would be better. 5.7L 7300 rpm with 450hp?
Destroked 6.3 as mentioned, with a wilder cam.
Oh, and the car should be 200lbs less.