While it is a common solution, welding here isn’t your best option.
In order to bond with the metal a weld needs to melt the cast-iron and in this case, there are a lot of carbons and deposits from the engine inside the manifold. No matter how good your weld is these contaminants are likely to cause your weld to crack.
Metal spray is considered to be the superior option in this case because the spray is ‘surface alloying’ and doesn’t melt the cast iron to bond with it.
The video demonstrates how to use Eutalloy 10224 and a Super-Jet oxy-acetylene thermal spray torch to repair a cast iron manifold.