I asked about this one not long ago flea. http://www.eastsideboxing.com/forum/showthread.php?t=153505&highlight=chang Between RB and sweet_scientist's post you should get a pretty good idea of what kind of fight it probably would have been.
I've seen a lot more of both now :yep In a 'prime for prime' matchup Chang would be too much of a force but Yuh was so class all-round he's in it all the way. Anything other than the very best Chang and Yuh could edge it. But Chang has the edge in speed, is just more jazzier in contrast to Yuh's technical pressure/ring generalship combo. Would've been a truly great fight I'm sure. Chang is the greater fighter and more impressive on film for me.