I have the mbrp 2 1/2" on my ZX3 with a trubendz 2 1/2 " flex pipe , it bolted right up!
it will be loud without the cat, but you get used to it. i like it[thumb]
With the shorty header you're still gonna need an off-road pipe to go from your header to your flex pipe! hope that helps. btw just be sure to get a zx3 flex pipe, the svtf is the same after the flex p. dimentionally. if the hangers don't match up any shop can hang your exhaust for ya for a small fee.