Just watched a recent rebroadcast of the episode, What Say? In a part of it there was someone using ASL while Mr. Cosby was speaking and explaining it. I didn't catch if they mentioned who he was, but he looked like Jimmy Walker. Am I correct in this? I checked credits online and found nothing.
http://www.dlbach.com/
I just put in the DVD for that episode and the guy doing the sign language is definitely not Jimmie Walker.
He's more muscular his face was wider and looked younger than Jimmie Walker would have been in 1976. This guy looked like he was about 24-25.
Jimmie Walker was almost 27 when Good Times premiered in 1974. He would have been 29 in 1976 when this episode of Fat Albert aired.
The man wasn't credited at the end of the episode either, which is probably why isn't credited on IMDb.
Here's a picture of the guy in the episode:
http://i62.tinypic.com/erzuq9.jpg
This is Jimmie Walker from around the same time:
http://content8.flixster.com/photo/14/11/23/14112358_ori.jpg
(knock,knock,knock) Penny (knock,knock,knock) Penny (knock,knock,knock) Penny
That man doesn't look anything like Jimmie Walker!