I have been looking at a series of '08 articles/photos on this site concerning splitting a cast iron exhaust manifold. The author was treating the manifold as if it was cast gray iron as used in blocks and transmission cases (preheating, short welds, peening, slow cooling, etc)- which IS required for those gray iron parts. No problem, but its VERY labor intensive and not required at all.
The cast iron as used in exhaust manifolds is more like maleable cast iron and can be arc welded as normally as welding steel (almost) using nickle welding rods, and if the manifold has not had the "carbon" burned out of it (usually will look VERY RUSTY and quite Orange in color, when compared to an almost shiney cast iron exhaust manifold on a new car)then it will not be a problem (the problem being that all you can do with a stick welder to "burned-out" exhaust manifolds is burn a hole in it rather than able to deposit weld material) to weld to the manifold.
Thru the years I have used two types of new outlet materials. The earlier outlets were fabricated from a short pc of steel pipe with a home made plate flange welded to the pipe.( this assy was then welded to the cast manifold after burning a hole in the cast and grinding everything to fit). Later we even used steel tubing with a flange (like a stock Head pipe) assy welded to the cast.
Two welders have done this for me (the old timer - a lifelong aircraft welder taught the current guy - a carpenter how to do it) with equal success.
Save all the care and attention to details where it is needed welding up cracked blocks, transmission cases and INTAKE manifold as the exhaust manifolds dont need it.
