4.6L Sohc to 5.4L Sohc worth it?

[UtOhCop]

I'm looking at a 99 Saleen and i was thinking about different mods. How much of a torque increase would i be looking at by going to the 5.4L? Ofcourse i'd like to throw on some Crower cams and ported heads while i have the engine being assembled.