Hey KWhite,
Unfortunately like I said before our first gen. 4.6's are weaker than the 99 and up. Your 96GT pumps out 215hp stock. The 98's had 225 and the 99 and ups have 260. The 425hp is most likely on a 99 or 01 Cobra (or possibly a GT with other mods). That's not to say that a supercharger isn't the way to go though. Hammer (the moderator in the forum) just went through all this plus different heads and intake and some other goodies and he is pumping out some serious numbers.
Brett
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66 Tahoe Turquoise Coupe
Laser Red 96GT Ragtop
30 Years & 30 inches apart in the driveway!