The more I think about it the more I favor a y pipe that runs simular to the stock setup without the expansion chamber or dumping into the driver's side manifold. Main reasons being:
-No heat on starters
-No burnt floor mats
-No risk of rock rash (these are 4x4's after all)
-Cheeper to produce
-Easy to retain stock o2 location.
-Easy to retain stock cat location.
-No heat transfer to tranny
-Overall better us of space.
I really don't see any major negatives to this plan and it would bring the cost down from the ~$200 range to probably the $150 or less range (depending entirely on the cost of parts of course).