Headers will only help. You might want to talk to your engine builder now and get his opinion.

I agree, talk to your engine builder or supercharger distributer. Headers will definitely help but is the additional money worth the increased HP. All boils down to how much you want to spend.

You may also want to do a search on OSO for DANA exhaust, don't know much about them put they look good for the money.

I had a set of EMI on a 502 EFI Mag. I did not like them as much as the GIL's I had on my other boat or the CMI's I have on my current boat. My ex son in law has SM with long riser/pipe combo on his 540's and the seem to work well. Any exhaust that uses the jumper hose from manifold/header to pipe needs to be checked every year for colaspe. I have found this more than once. Joe Murray

CMIs are worth the money. There are many different models to fit most budgets and applications.

I swapped over from an old stock log style manifold to Dana's. The only reason I picked Dana's over the others is I like the way they look. I think all aftermarket exhaust are going to be close in performance. I'd say headers if you want to spend that kind of money, and if you are making enough power to really make use of them. If nothing else, I save 90 pounds swapping the exhaust.

I had EMI's on an SBC I was running. I really liked the way they sounded.

I changed over my stock cast iron exhaust to SM. Seen no difference in performance, nor was I expecting to, but I did loose around 80#'s. Stock 502 EFI's with silent choice.

I did a lot of research on this matter myself. I chose the
Dana Marines for silent choice system. The Danas and the
EMIs can be colored to your taste. I wanted this over a
standard black manifold. The Stainless Marine choice is an
excellent one and I heard of great customer service. I ordered
my Danas in October and I still do not have them on my engine
due to oil line/filter interference issues and missing parts. I
was assured before I ordered them that there were no known
installation problems. It is now mid January and I still have
no solution from the guys at Dana Marine. Bob at Dana knows
of the problems and said a solution is imminent. I will wait
a few more weeks then I think I will have to send them back.
I really like the way they look and the Danas were highly
recommended to me by Ray at Raylar. I thought I made a
great choice, but perhaps not. They do look good though!!!
Stock Merc 502 Mag MPI.
O.K. maybe my mechanic is not the most knowledgable, but
she works all day for a Mickey Mouse pancake and a side of
bacon.

I have SM on mine that have about 400 hours on them-took one apart in September to replace a gasket and they look brand new inside. I do flush pretty regularly but was pretty impressed by what I saw.