what do I do about the exhaust? Obviously I have the H23 header and cat and that's it right now. Will my stock exhaust work by using an adapter plate or something to have it bolt up to the prelude cat? or do I have to get a custom exhaust made?

 

I believe the H23 header and cat are going to be longer than the stock one that you had before, so the exhaust pipe and cat won't bolt up. You'll have to cut and weld your exhaust pipe shorter so it'll bolt to the cat.