Well, for that I will have to say I'm not a huge Filmation fan, but I just absolutely love Fat Albert. While they did a terrible job adapting things like Tex Avery's Droopy and Tom and Jerry (though I remember liking their Mighty Mouse), Fat Albert was the best thing the studio ever did, IMO.
Lou and his family did many voices for that one. Bill Cosby and 2 kids (whose names escape me at the moment) did most of the voices, but the family also had a few roles. Lou's biggest role would be Dumb Donald (my favorite character), which he took on after the 1969 special "hey Hey Hey! It's Fat Albert" in which he did Donald's voice. it was one line, so it would have been rediculous to pay an actor to do one line. After that, he was made Dumb Donald. He also played Stinger, the brown Hornet's sidekick, Legal Eagle, and various adults. Apparently, he was really modest about this.
his wife did the voices of both teachers, Mrs Bryfogle, and the blonde one who I can't remember the name to. His Daughter voiced several girls in the show, and Tweeterbelle.