The automatic runs into a lot of issues. The tranny is 7500 bucks or so (I've had 3 of them). You can run either SC on low boost with stock internals, but if you plan on beating on it, you need to rip the motor out. Upgrading the internals, assuming you provide the block/crank will run about 10 grand. That's for a spinning assembly (rods/pistons/mains/cams), you'll still need to upgrade your valvetrain. If I recall, my motor was about 15k, but that counted the strikers. So once you get the motor done, then you get to buy the supercharger. You got the tranny working, so what's next? The rearend with the smaller brakes so you can actually run a slick. Those new rims/slicks/rearend will run about 4k total.
The good news is when you hook all this massive amount of power up in either application (paxton/roe), you'll may twist your block in half from all the torque. When you hook up the type of power you're making, it will find the weakest link in your build. Remember, this isn't a 3500lb car, it's a 6k/lb truck, everything is different.
If I were you, I'd run VERY minimal boost, keep everything stock internally. I'd search the forum for the posts stinker made about upgrading some internals on the automatic tranny. Realize you'll be limited at the race track due to the tire issue, but last time I checked you don't use slicks on the interstate.
