Differences between Gil exhaust manifolds and 496 exhaust manifolds?
 

I am looking for 2 pair of dry joint exhaust manifolds for my turbo engines and was wondering what the differences between the Gil exhaust manifolds and the 496 exhaust manifolds are? Do one pair flow better than another? Is one brand more susceptible to corrosion issues than another? I hear that the 496 manifolds were available in aluminum and iron. And the iron one had 2 different kinds of water inlets on the bottom. Were the Gils only in aluminum?