I don't know about them NOT being a header, this data is straight from the IMCO website:


As high performance marine engines grow larger in displacement, so does the need for a highly efficient and yet affordable marine exhaust system. To meet this demand, the innovative engineers at IMCO have the new PowerFlow Plus cast aluminum, fully jacketed, exhaust manifolds.
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PowerFlow Plus manifolds include the superior advantages of the PowerFlow exhaust system described above, plus the additional features necessary to handle 600 to 1300 hp.
With patented design, 33" internal runners and an ultra hi-flow exhaust riser, you can bet that this exhaust will match or exceed the performance of racing style dry-stack collector headers.

PowerFlow Plus represents a major breakthrough in cast aluminum manifolds and risers with the strength to match or exceed anything produced and the reliability to last through years of operation. PowerFlow Plus exhaust systems are used by major racing teams and prominent engine builders alike."

I would use KE's headers, but I don't want to cut my deck/ swim platform to get them to fit. And I might still look into the KEs, they have worked great for me in the past.
I like the looks of CMIs, but I seen/heard too many people who had weld problems with CMIs, Stellings, Lightings. IMHO

So, who has the best $$ on IMCO's
Thanks,
Dean

Not exactly sure what your main goal is but Revolution Marine has been around for a while now and they offer a great alternative to GIL/IMCO Manifolds. They look very similar. They do sell on ebay as well (sometimes factory blems). Never seen them in person but they sound as good as any of the cast aluminum. Looks like this ebay ad you can have a set for $1,100 delivered to your door!

http://cgi.ebay.com/ebaymotors/Revol...spagenameZWDVW

www.revolutionmarine.com

Let us know what you decide!!!

Dave

If you are looking for a new system we offer IMCO systems at our everyday low price, you can get more info and pricing on our website here.
I think the IMCO would be a great choice for your application but nothing below that.
And to add to the failing weld problems, I have been here for a little over 2 years and I have never heard of a Lightning header with weld problems.
Please PM us if you are interested in a exhaust system and I will quote you a OSO member discounted price.

Thanks,
Brad