It can be brazed or welded, but would need controlled pre and post heat, and would have to be resurfaced after welding.
Exhaust manifolds also get loaded with carbon, making for a more difficult good weld.
I wouldn't attempt it, you could find a used replacement or a tube header for probably what you would invest in an "iffy" repair.
Having said (typed) that, if you can find a welding shop that does commercial or farm equipment repair and do cast iron work, it may be worth an inquiry.
If you do decide to attempt to do it, V the edges, clean the heck out of it, clamp it rigid, and make sure there is enough heat in it, pre & post.
Then listen to it as it cools... tink... tink... tink...
: 68 spitfire Mk3: Been so happy since the
: pcv valve was sorted I knew Karma was
: out to get me... The front branch of
: the cast iron exhaust manifold cracked
: clean off. Anyone ever weld or had one
: welded? I can mig, tig or braze. How
: did you do it?