The long and short of it is you might be able to go to one cat that is high flow but I would be wary of it on the later series (1fze motor) as they are obdII compliant with the second 02 sensor. make sure the cat is designed to be able to filter enough so that it will not impede the performance of the secondary 02 sensor.
Are you kidding? Did you know that 80% of the Dodges, Fords and Chevy's have both manifolds connected and then Y them at the rear for sound, you didn't really think they were REAL dual exhaust systems.
Boy, two cats look like they are worth their weight in gold.