That's the proven set-up from the 2000 Cobra R right ?
5.4 liter, NA, 4 valve.
Seems to me that there are more likely combos that would fall in between the '07 Shelby GT500's Supercharged 5.4 liter monster and the standard GT's 4.6 liter, 3 valve.
Namely:
4.6 liter, 3 valve SOHC, supercharged.
4.6 liter, 4 valve DOHC, supercharged,
5.0 liter cammer (perfect for a BOSS reintroduction); same as the GTR's engine.