A few things off the top of my head...the most major change that I recall is that the complicated through-the-engine clutch rod (like the ones that XXS650's have) was eliminated, and replaced by a much simpler external clutch lever on the right side of the engine, some different (improved) internal clutch parts, a few tweaks to the transmission, I think the oil system was modified a bit, too...
That's all I can recall from my CB550...