the cb500 exahust may interchange with the 74-76 cb550K since the frames are different but the 75-76 cb550F exhaust won't work at the muffler because the rear pegs mounting locations are different and the exhaust will interfere with the sidestands.
the 82-1983 cb650 nighthawk chain drive uses the same motor as the cb650 which may work with the cb500 but something tells me the exhaust spacing is different. At any rate if the headpipes fit the rear bracket most assuredly will not and something will have to be fabbed. Any other nighthawk is no bueno.
I'm not too concerned about the rear mounting brackets, I can always fab those. I was just curious if they had the same space between pipes and if they would clear under the frame. Just wondering if you could make it work without too much difficulty.