Yes, I welded my intake and exhaust manifolds with NiCad rod. You can braze them but you have to get the metal real clean and use flux so the brass sticks to the cast iron. Also, they may warp some from the heat so you will have to remachine the surface that bolts to the block.
If your not good at welding have an experienced welder do it. when you machine the surface of the ports you have to have both manifolds bolted together so they align correctly.
