Chonan only weighed 182 lbs for his fight with Silva, and should be able to cut and make 170, where IMHO he'd be an absolute beast for anyone in that class.
All he'd need to do is lose a few lbs, cut the rest the day of the weigh ins, and he'd be in at welterweight.
What did we see when Sakurai fought Trigg? I don't know what you saw, but I witnessed a GREAT fight where Trigg dominated in the beginning but Sakurai, being the man he is, stood tough and was able to come back and catch Trigg with a great punch. I'm sure Sakurai had all the respect in the world for Trigg then and now.
I dunno know if he could take Trigg because under 170, outside of Hughes, I dont think anyone can really (i would favour Trigg over BJ).
I guess it just comes down to whether Chonan will continue to fight in Pride and if he will fight guys close to weight (ie. not start taking on Silva, Rampage, etc.).
Not 100% sure if he trained them of not, but if he did Kyoshi Tamura's ability as a trainer is pretty damn good. He has produced some damn good fighters (Ryo Chonan being the most well known to "mma fans" in the US. Daisuke Nakamura is also a damn good fighter that most people will probly never get a chance to see)