The gaskets have a similarity to a bottle cap. A material that is a standard manifold gasket fits in the bottle cap and it slides over the end of the manifold. If the manifold is badly rusted, I put the manifold in my mill and cut all the opening down until they were the same height and have good metal. No mill? Any machine shop could do this.
If you need seals, they are available on this sight for $11.90, Part No: 70229958. Go to tractor parts under marketplace.