3.5 Pulley Swap

Just bought a supercharged 06 GT, and I was wondering what supporting mods would be required for a 3.5" pulley switch. I was considering a 3.4, but I from what I've read, it would need a fair amount of supporting mods over the 3.5, and since I don't really have all to much in the way of money, the 3.5 is looking good. I know the obvious: CAI, cold therm, and plugs. I guess my real question is: Do I absolutely have to have a 3" down pipe? If not, what would I have to do instead (if anything at all?) I have access to a scanner, so I can readily check on my KR, no need to worry about that. Any help would be greatly appreciated. Also, where could I get any supporting mods/a swap kit? As you can probably tell, I'm rather new to this, so I will not be doing the full install myself.

If your limited in cash skip the pulley and go for the 3" DP with high flow cat. Also a tune will really waken that beast up. GM programmed alot of torque limiting in those models so much that the previous gens were faster with less power. The 3" DP is a good base to build from. Since all the other mods have to go through their anyways.

Hmm, I'll keep this in mind. Thanks for the info.