Chevy 350 exhaust manifold question?

My Chevy 350 has old exhaust manifolds that have a hole in the passenger side one for the old style draft tube I believe it was called. I do not use this as I have a pcv valve and a breather cap in my valve covers. I think the strong stench of exhaust fumes I get every time I drive is partly due to that opening. 

Does anyone know if there is a type of plug for this or does it need to be welded?