555R

I would like to know if there is an air flow difference between a stock b-16 exhaust manifold and a stock gsr exhaust manifold and an after market gsr header? Here are my questions:
1. I just bought a Greddy Power Extreme cat back exhaust for my fifth gen hatch. Which pieces will bolt right up together including the cat. B-16 manifold-cat- exhaust system? Or gsr header-cat- exhaust system. I know from other friends hybrids that the gsr-cat-exhaust needs an extension piece between the cat and exhaust since the gsr header is almost 6 inches shorter than the b-16 manifold.

2. How much more restrictive is the b-16 manifold than the gsr header when mating it to a b-18 gsr swap?

Thanks, Joe