The problem is not so much the heads and/or the gaskets but in the use of cast iron exhaust manifolds. Using gaskets in conjunction with the cast iron manifolds does speed up the frequency of broken or cracked manifolds. A thin film of hi-temp RTV in lieu of using any form of exhaust gasket seems to prolong the life of the manifolds. Gaskets used with headers should not present any problems other than potentially being more difficult to cleanup the flanges when gasket replacement is required.

On my Y powered roadster with aluminum heads and with steel header flanges, I do use high temperature RTVand no gasket. I do see evidence of some impressions being made in the cylinder head where the raised portion of the weld on the head side of the header is imprinting itself into the aluminum heads. That will be a problem down the road. On the dyno when using aluminum heads and headers, I do use copper exhaust gaskets but those do have a tendency to leak.

With the exhaust manifolds being machined flat at the head mounting surface, then a thin film of RTV should suffice. For the same reasons the manifolds break when using gaskets with the iron heads, the manifolds will also break or crack when using them on aluminum heads with gaskets. Keep in mind that the exhaust manifolds for many of the as delivered Ford engines did not use any form of exhaust gasket at the heads and simply relied on a good metal to metal fitment.