Hanna-Barbera had attempted to get back into primetime well before the short-lived Hanna-Barbera Happy Hour made a cameo appearance on NBC in the late 70's. Unfortunately, their family-centric cartoon, Duffy's Dozen, never got past the pilot stage.
The clip opens with Bill Hanna & Joe Barbera, appearing in sketch form on the screen while the execs do the talking, making their pitch. 12 adopted children and a sheepdog create a very big family for the parents (Janet Waldo & John Stephenson). Duffy's Dozen didn't sell, but Hanna-Barbera, undaunted, went with a big family the next year, by adapting the adventures of a certain Hawaiian detective. Yep, subtract two kids, turn the sheepdog into a smaller breed, subtract the mother, and you have The Amazing Chan & the Chan Clan.
Casey Kasem not only voices one of the boys, Alan, but is also the park ranger and the end-of-pitch announcer.
I think you can see why this didn't work out.