Old Coes,
It looks like you have done some research yourself. I have limited experience with cast iron...here are my thoughts.
Cast iron is very high in carbon, this is the obstacle in welding it. When you weld it and melt the parent material, you change it metallurgically. This results in a hard brittle area know as martinsite adjacent to the weld. This area usually fails, or cracks.
I usually only braze cast iron..this doesn't bring the base material to a molten state which keeps it intact metallurgically speaking. The brass melts at a much lower temp than the cast iron.
It isn't unusual to arc weld cast iron using high nickel rods or special "pulse" electrodes made for this purpose. If the part is small enough, or the furnace large enough, the part is preheated, welded, then post heated to relieve stress and negate the HAZ, or heat affected zone.
I think the "stitching" process involves threaded studs that are screwed into drilled and tapped holes in cracked castings..heads etc. These plugs overlap each other and form a chain of new material.
If your Mack block has actual "pieces", this will have to be a weld repair. If the repair is to be visible, brazing might not be the process you want. The quality of the casting can make a big difference in the ability to weld repair it, and the finished quality of the repair.
It would not be unheard of the send a naked block to a experienced welding shop for repair..I would assume you wouldn't find a new block at your FLAPS!
Make sure the block is not broken and useless somewhere else, like a bulge in a cylinder. To work, the repair will have to be done by a experienced shop who does this sort of repair. You will have to be prepared to pay for their expertise.
Stuart
