i think i would look at the eddie marine emi exhaust for that application first.. it doesn't have the choke points that stock manifolds have so it should help flow. but your not paying double for those long runners that aren't going to help that much. although the photos' look like the risers are different from stock.
Don

Cmi makes excellent 4 tube stainless headers and they can add power 30-50Hp to almost any high performance BBC marine engine with proper application.. The type of header you run with supercharging is not as critical as it is with a N/A motor. If it were my boat and motor I would look at the Stainless Marine High Torque Three, CMI Etops, or Dana Marine Manifolds with big tube collector riser. These units have larger volume risers and should work as good as it gets for supercharger exhaust blowdown. They are also significantly less expensive than long tube stainless units.

My two cents.

Ray @ Raylar

Ok, call me stupid but will they fit ?

I thought (cause I don't know) the 496 kit was the only ones that would fit.

Betitbig:

I would measure from the top of your existing stock exhaust risers up to the bottom of your closed hatch. Thats how much top clearance you have if any. Then measure from the top of these stock risers down to the level of a line running through bolts that bolt the manifold to the cylinder head. This dimension can then be checked by any header or manifold supplier against their dimension and tell you if those headers or manifolds will fit. "Measure twice, cut Once!"

Ray @ Raylar

I will be on the dino in a week or so.I also have the same cam as you ,same computer program and 3.3 comp .We 708 hp 8#s boost with 2.3 compressor.Tyler Crockets doing my work now. and we will dino with stock and cmi,s also.Tyler also said etops would work the best I,ve been following your engine biuld thru Larry and Dustin. Those are some great no.s what size pulleys are you using.

Hey Robert, how are you doing...

I am happy with the numbers so far, now to just get it in back in the water again. I am now looking at the CMI e-tops because as you know, good is never good enough.

Im going to Larry's this Monday to pick up the boat and spare (for sale) 2.3 motor. The 2.3 made 640hp with 6 1/2lbs of boost, with dyno time only so far, and hopefully some will want to pick it up.

One of the most important factors which you should consider with the CMI's is your cylinder temp should run a litte cooler for sure than those stock manifolds. Thanks Cam-shaft.

Go with Stainless Marine Gen III for the supercharged engines. They have been proven to provide more power and torque over the headers.