I know all about them ... I put something like 50-60,000 miles on one of those (no odo)... (it was actually a CB500 chassis with a later year CB550 motor in it)
had a Yosh cam and a J&R pipe and a Martek CDI ... was way faster than a stock CB550 ... those stocker are just s l u g g i s h (the cam really makes it come alive).
also had S&W air shocks and extended fork tubes with Magura clipons above the top triples
.... still have every bit of it ... I think it either snapped a cam-chain ... or it dropped a valve ... at a dead slow 'idle' - (slower than idle speed)
Since virtually everything on the bike was totally worn out ... I just parked it ... I just removed a mirror from it a few days ago.
Mine was stripped down ... weighed like 405 to 409 pounds
lotsa miles and years on that bike ... I couldn't complain about it.
They don't handle very good ... feels like the h-bars are welded to the frame ... too much trail - maybe