There's a gasket between your head and the manifold, and there's a gasket between your catalytic converter and your manifold. They're not reusable. Well... they could be, but if you develop an exhaust leak because you didn't have them, there goes your pretty paint job, and fast. Get the torque specs for the manifold and converter nuts before you begin. Snapping one of those would not be fun. Just trying to save you a headache.

Hondaman is right. My CX stuff didn't fit a DX motor. I had to change a lot of crap. You would need a new header, cat, a EX/DX or even a CRX downpipe, and I believe the mid-pipes are the same. The factory hangers won't line up when you're done, either. You'll have to get creative. If you can't find it in a U-pull-it junkyard somewhere, that stuff may be difficult or expensive to find.