This is a rare feat. Two actors (Ron Howard & Donny Most) leave the parent prime time series & end up voicing on the Saturday AM series. Donny would later get another Saturday morning gig on Dungeons & Dragons (with Willie Aames & Adam Rich).
Henry Winkler is one of the few actors to do a prime time series & the Saturday AM version in the same season (The Brady Bunch kids & Punky Brewster also hold that distinction).
Closing credits could not be found on this series until after The Richie Rich/Scooby & Scrappy Doo Hour. Except for Superfriends & the Weekend Special, ABC had the idea to merge one set of closing credits for three shows (or as I would call it, a prize package). There were two sets, one was for the Hanna-Barbera set (Fonz & The Happy Days Gang/Richie Rich/Scooby & Scrappy Doo Hour), the other for Ruby-Spears (Thundarr/Heathcliff & Dingbat/Plastic Man & Baby Plas).