The reason why I asked... Is my engine builder has a set of requirements for the engine for the headers.
They are... do the headers as a step, 2”to 2 1/8, with each segment 15.75 to 17.25” if you have enough room. If you use a merge collector you want the throat to be 3.25-3.5 with a 4” outlet. Standard collector should be 4”. Best tuned lengths (end of primary to end of sidepipe) would be 34.5, 68.5 or 137.5” long.