Early A-body Headers

I do not see advantage of stuffing those ugly headders into my 65 cuda? WHere is defineable flow testing to tell me I gain Hp on my 318. The cuda runs great with my original exhaust manifolds with heat risers cut out. I can still change plugs and car puts out plenty of power, where is the gain from these headders? What does the dyno show compared to stock exhaust? I could spend that money to do other things!! I have a custome done dual exhaust that flows great, I would have to redo that also costing more money to redo welds existing. It does not compute to spend money not needed! I can use that for body, paint,cam ect. No gain = bad investment!!!