There's a 98% chance that the sealing surfaces are warped. Even on the manifolds that are not cracked. If you put warped manifolds back on, they usually crack because cast iron isn't exactly very flexible. So any exhaust manifold you want to re-use should at least be fly-cut (milled) flat.
When you get the ear welded back on, the bolt hole will need reaming out and the entire face will need to be milled.
And no, J-B weld won't work.
