This has been discussed at length in previous threads. Unfortunately, I'm not able to pull that reference up for you at this moment.
Ford did not use gaskets when the engines were originally built. Most every replacement gasket set for y-blocks has exhaust manifold gaskets.
IF you have FoMoCo cast iron exhaust manifolds, do not use exhaust manifold gaskets with the FoMoCo cast iron cylinder heads. When used, exhaust manifold gaskets reduce the heat transfer between the cylinder heads and the cast iron exhaust manifolds resulting in an increase in the likelihood that a crack will develop in the exhaust manifold. Exhaust manifold cracks in the 'ears' that secure the manifold to the cylinder head seem to be the most common.
The often recommended 'sealer' for exhaust manifolds to cylinder heads is graphite grease. Some have mentioned the use of an RTV sealant, but I can't speak to that.
IF you search the Forum Archive, I'm sure that you can find recent threads on the subject of exhaust manifold gaskets. Hope this helps.