What type of metal is the exhaust manifold?
I've got a friend who cut his catalytic converter off this car.
He says it bolted to the manifold and he wants me to weld
pipe to it and replace the area where the converter was.
Question is what's the manifold made of? Is it cast
aluminum or cast iron or what?
Typically cast iron.
Could be done but wouldn't it be better to bolt the manifold to another cat mounting plate and then weld the pipe replacement between it and the other end of the exhaust pipe? It would be easier to work on down the road.
Even if you manage to get a clean weld (nearly impossible to cast iron) the weld will crack. Use the proper flange and donut seal.