His assist and blocks tend to fluctuate so far in his career, but I'd say in his prime he'll get a max of 2.5 assists and 3 blocks.
I think his low assist average has a lot to do with Van Gundy's system. Yao is very underrated passer. Remember all those no-look-behind-the-head passes while Yao was a rookie with Rudy T. as coach? Another thing...the Rockets "shooters" failed him miserably this season. I felt sorry for the guy, since he played his heart out, but received zero help. In the postgame interviews, all the chumps would say stuff like "we need to help Yao out, we need to hit our open shot," yet they come right back the next game and pull the same shit. Lets hope TMac can get healthy and the management brings in some young guns.