Hy Cougar, there are flange gaskets which are flat on one side and domed on the other side, if you post the I.D. of the manifold I can provide you a Walker part number for this type of flange gasket, hope that helps.
The only numbers I see on the exhaust manifold are on the right hand side near the #6 runner. It has a large GM600 with 328 below the GM600 and 44 on the #6 runner itself. The only other numbers are on the intake. Are these the numbers you need?
