I would run 3" pipe (even though 2.5 would be enough). If you decide on 2.5" (for more ground clearance) then use mandrel bends. A 2.5" system built with mandrel bends will flow like a 3 inch system using crushed pipe.
Make a H or X pipe right after the transmission the use a pair of hooker aero-chambers. If it is too loud, install a pair of 12"x 4" dynomax bullets in line (before the mufflers would be best but after also works).
If you decide you want to quiet and good flow, then install a set of dynomax super turbos.