Quite a bit of work for no gain, but no reason not to if you know a GOOD mandrel bend shop.
Don't get too creative because there have been some problems with emissions and engine codes setting due to changes in the exhaust flow which trip a catalytic convertor efficiency SES light.
The pipe to the cat and from the cat is about 2 1/2" and the Y and outlets vary from 1 5/8" to 2" because of the way the benders crimp the bends.
For my .02, duplicate the setup in 3" to a 2 1/2" Y with a good set of s/s mufflers and CORSA tips.
www.corsaperformance.com