For welding, the best, bar none, is Chris Razor, Hi Tek Welding, 734 414 1994, in Plymouth, Michigan. When he welds cast iron, he uses a system developed for repairing the giant ladles used in steel-making. Last I knew, he was a co-owner of the necessary equipment along with Jack Roush, who is his partner in the stuff. Chris does their specialty work.
Back in 1990, FoMoCo built a running prototype/show car and called it the GT 90. It was powered by a V-12 version of the four-cam V-8. The crank and cams were billets made for the purpose, but the block and heads were made by lopping the front two cylinders off one set of castings and the back two off another set. Chris Razor welded the two sets of six together to make a 12 cylinder running engine. The engine had four turbos on it.
I have seen Chris run a perfect bead on the sharp edge of a razor blade.
KS