Clamp the modified manifold into a horizontal band saw and cut the original flange off. Scrap the rest of it. The old school way to make a split manifold was to use a 1 1/4" cast iron pipe elbow, cut a hole in the side of the rear manifold runner with a hole saw a couple of inches behind the original flange, and weld the elbow onto the manifold at an angle to match the original exhaust pipe. Then weld the flange onto the elbow, and add the divider between the runners by slotting the runner between the outlets with a cutoff wheel and welding in a chunk of cast iron scavenged from a donor manifold to fill the slot. That way, all the metal is of a pretty similar alloy, and the welding is a lot simpler. Use nickel alloy welding rod, and preheat- - -weld- - -post heat- - -peen- - - -about 3/4" at a time. Repeat as necessary until the welding is complete, then bury the manifold in a pile of sand overnight to cool down slowly. You'll end up with an exhaust system that looks like it was made in the 1950's- - - -and the heat riser still works.
Jerry
