A 408 is definitely going to give you a ton of power, however that is going to require a ton of supporting mods to match the build. I think you should get a magnacharger as has been suggested previously. The reality of the fact is your going to have to spend a lot of money to get that thing moving.
I think you should do a few things at a time and see how you feel about it.
In this order a very good start.
1) Custom Tune
2) Bolt on's (CAI, Exhaust, etc)
3) Gears (4.10's if shorter tire than 31.5" or at least 4.56's for anything taller than 31.5")
4) Stall and Cooler
5) Cam
6) FI or more cubes
7) Both FI and more cubes
Note: If you are going beyond Step4 plan on getting a bunch of supporting mods. (Fuel, trans, etc)