Long before the Fenton (and other) split header systems became popular, people would weld a second exhaust pipe flange onto the stovebolt exhaust manifold and weld a blocker plate in, creating a "split" manifold. Done properly, each cylinder in the firing order used a different pipe- - - -1,2,and 3 down the front pipe, and 4,5,and 6 from the rear. Because of the firing order, the exhaust pulses alternated from one pipe to the other. Some people think splitting a stock manifold is better than using Fentons, since the heat riser stays functional and it's not necessary to cobble up some sort of carburetor heat system.
Jerry
