I just read that ultimately you want to have a rear cat delete, if you purchased the off road SW headers you will have no cats on the car whatsoever and your current cats are too small in diameter to properly fit(choke point) in the lead pipes. You will need custom work to make them fit. My advice would be to just buy the catted system.
2003 Black - sold, back again, and sold
2003 DBP/DC - #153 Whipple 3.4 (permanent garage art)
2003 DBP/LF - # 36 (sold)
2003 DBP/LF - # 205 (sold)
2004 Black - Trilogy #43
2003 Black - shitbox (sold)
2004 DTR - shitbox #2