BB exhaust manifold question

[cheyenne10]

I am using a pair of stock exhaust manifolds on 454 BB. These have the flat surface where exhaust mates up to them. Am I supposed to run the exhaust preheat valves (can't remember specific name) on these? I am worried about warmup times and also the need for good gasket from manifold to exhaust pipe. If I remember the preheat flapper extensions have the bevel end for use of the donut style gaskets. I don't want to end up with leaks with lessor gasket on flat surface mate up.