I'm pretty sure I have CB650 forks on my CB500. I didn't do the swap, it came that way in some attempt to make it look like a chopper or something. You might want to measure but I think the 650 forks might be a little longer. Are you trying to swap just the fork tubes or the wheel also? Also the triple?
Easiest swap is take the whole 550 front off including the triples and then just bolt in the 650 front end. It might be possible to not use the 650 triples and then just slide in the tubes into the 550 triples if the fork spacing is the same on those 2 models. I think it is but would have to double check.
That list on ohiocaferacer is a decent one. I compiled it about 2 years ago.
There are a few errors though that I really should have fixed. I also have a list of steering stem diameters that helps out when you want to do stem swaps.