You'll probably have to do some welding if you're trying to bolt it to GReddy piping. The axle-back section of the ITR exhaust uses a 2-bolt flange with flexible gasket and those springy bolts. Your GReddy piping probably uses 3-bolt flanges w/ regular bolts and a crush gasket. The ITR axle-back section might also be a bit short, since 4dr Integras have slightly longer exhausts. You can weld a 3-bolt flange onto the ITR axle-back so it'll bolt to the GReddy piping, or you can get the entire ITR cat-back and lengthen some of the piping. If you don't mind keeping your SP and just want it to be quieter, you can get an inline resonator welded into the A-pipe, which will quiet it down. If you already have a resonator there, you can weld an additional one in downstream a bit.