[dwtaylorpdx]

Order the cast iron nickle rod from Lincoln. Youll need a stick welder and the knowhow to weld.

Prep the crack, it needs ground to a V about 1/2 the thickness of the metal.

Heat up manifold in a oven for a couple hours,, pre clean well your baking the contamination off. Having it chemically dipped first helps.

Put a torch inside the manifold to keep the heat up

Weld with the stick rod.

Have a box ready with about 3" of sand in the bottom
after you finish the weld, put the manifold in the box on the sand and cover with sand.
Let cool down for 8 hours or better yet just leave it over night..

I've done a couple tractor exhaust manifold like this and they lasted years.

Cleanliness is critical..