I’ve owned my welding shop for over 26 years and those are not cast iron. More like cast steel and crap steel to boot. I’ve tried to weld manifolds and every one breaks down the road just after the weld. Now cast iron radiators for houses with 100% success. I’ve even welded a few cast iron pans and parts for others with 100% happy. Because the formula for welding cast iron is easy.
Manifolds can be done, but just not by anyone. My attitude is return the manifold and find a header for that slant. You will never look back. My opinion only.
Good luck!
SN: pre grind cracks or plated cuts like your case. Heat part to 400 degrees in oven for 30-60 mins dependent on thickness of part.
Braze or stick weld with Ni-rod” not letting part cool down. (Throwback in oven multiple times to maintain temp throughout welding time.) once done welding back in oven to 400 f for another 60mins to stabilize part. Then shut off oven and don’t open door. Let cool over night for the slowest cool possible.
Next day tap gently with a small ball peen hammer to “distress” the metal. Check straightness and you should be good.
