Rebuilt 1953 mercury flathead. Used standard Felpro gasket set with "standard issue" head gaskets and now I have a head gasket leak. I am running Edelbrock aluminum heads, do I need a special head gasket? I sealed all the threads on the head studs and have a few weeping at the head nuts and also building pressure in the cooling system. I did a leak down test and really dont have any large variances from cyl to cyl. Motor runs great and does not overheat. Would like to know if aluminum heads take a specific gasket before I order. Thanks in advance for any help.