Patching a Manifold is not a good bet, they are built with an inner exhaust manifold, a water jacket ans an outer housing.
In a pinch we used to (70s) use grey marine tex and fiberglass cloth. But if the exhaust is cracked you will get water in the exhaust and could lose the engine. I bought a riser a couple of months ago, I would bet the manifold is.
After 5 1/2 years I hope the OP was able to resolve this.