The trouble with these cars is they are 10 lbs of $h!t in a 5 lb bag. Nothing fits, you'll have trouble fitting an undercar exhaust of any great size and according to my muffler supplier the 2 1/2" will flow an easy 450 HP 2" ain't gonna hurt that thing a bit.
http://www.classicchambered.com/clas...cts.html#cobra