I was at an aftermarket R&D facility and they were designing a header for the RSX type S while I was there. The head designer made 200 different sets of HAND made headers to dyno on the car. Making a header shouldn't be that hard, the only hard part I see would be to find the most beneficial bends. It's all about the bends baby!
With a decent exhaust system, it won't be a suprise to me if you gain 10-20 hp depending on what you get.