Okay, looked at and purchased the 550 today. It is a '78. It's a 550K, with just over 11,000 miles on it. This bike is pristine! Mufflers are shot, and it is running seriously rich (guy I got it from rebuilt carbs, I assume the floats are incorrect since one of the carbs is puking fuel constantly). But wow! It rides pretty good, feels way different than my 750. I actually feel a bit more comfortable on my 750, but that's probably because I'm used to it. Pics tomorrow!