farmall h manifold

Cast is difficult but not impossible to weld. Problem is the contraction of the weld material after it cools. It tends to create cracks. There are several newer rods that are made specifically for cast that help with the cracking issue. They are expensive. Last time I priced them I had to buy at least 3# and it was about $60 for the rod. Whether it's weldable would depend on how it's broke and where. I have welded engines and manifolds using cast rod. I have also brazed them. In fact my distillate manifold on my F-20 had 2 cracked flanges and I brazed them. After grinding and painting you can't tell it was ever damaged. Find a good welder and let them take a look at it.
In the attached picture both the left and right flange were broken clean off. After beveling all the joints to get full penetration I clamped the pieces back on and brazed them with a bronze rod and flux using oxy-acetylene. Then I ground it back to its original shape and re-drilled the holes.

Andy.