Longs generally are not OK with emmisions, you can install a shorty mid pipe with cats however make sure you can use Long Tube headers in your area. On that note, if you can always go Long Tube as they offer more power and a better sound.
If long tubes do not pass, than leave the headers as is, shorties generally are just a waste of $$
2003 Redfire V6,
Show: Smoked everything, cobra front bumper, gt rear bumper, rear decklid and lower valence blackout with black mustang letters, 5% rear front 15%, black 98 Cobra rims front, 95 Cobra R rear black with chrome lip, black scoops and spoiler and exhaust tips
Go: CAI, True Duals with flowmaster super 44's, Bama Tune, full suspension (lowered, 8.8, 4.10s, UCA, LCA, springs, CC plates)