I have the setup you're looking to do on my splitport tbird (3.8L N/A), except for after the 3" section I have 2.75" tailpipes. Here's what I used on mine:
2.25" Catco High Flow Cats
Magnaflow resonator (don't remember part number, but it is a dual 2.25" in/ single 3" out)
Single 3" pipe to dual 2.75" pipes just before pumpkin, with turndowns at the bumper
It sounds pretty good, and should sound even better on a V8.
-Rod