I called Ripple Rock Racers (again), and they were unable to clearly tell me what differences there were between their CB650 exhausts and the one for the CB500/550s. They could not tell me if the spigots were different sized (they should be), or if the tubing were larger diameter, only that the system was lower to clear the pan.
They did say the spacing between the header pipes was wider, which I find hard to believe. They likely meant the exhaust studs were spaced differently, but they doubled down on the pipe spread spacing.
So, except for the oil pan depth, will a 500/550 header, like a welded-up, 1 piece, 4-into-1 line up in a 650 head? Anyone ever try?