I'm not entirely sure furnace brazing is necessary. As there are no oil passages or structural members. I think you could use a parting compound on the top edge of the block. Then, using the block as a jig, use a rosebud to heat the two halves, then just braze the joint. Wait till it cools (slowly) unbolt it and do the bottom edge. The rods we have now, everdure (silicon bronze), weldco 17 (nickel silver), etc. Flow very well and can be TIG'd instead of torched. Something to consider. Weldco 17 has a Tensile strength of up to 95,000 psi, which is stronger than cast iron. I wonder if one of those Brazilian manifold T. Lowe has kicking around would bolt on? They have 6 intake ports.
