There indeed were two versions of not just Frank, but the entire family. The wife in the first version was named Oblivia, but then changed to Hidea. Both versions of the character looked the same though. The kids however, changed significantly. The daughter was originally named Hidea in the prime time shows, and was a teenager. In The Fred & Barney Show, the name changed to Atrocia and had an annoying cackle. The character changed again in the Flintstones Frolics series as here she was a young kid close in age to Wednesday Addams. She also had powers of witchcraft that could occasionally cause trouble, particularly in one episode where she made a clone of Fred to her father's annoyance. Frank's son Freaky was first seen as a pint-sized version of Frankenstone, but again in the Frolics series, he became the teenage son who seemed to be the male version of Marilyn Munster.
And indeed on topic, R.I.P. Mr. Reilly. Other than the above-mentioned shows he voiced, I do remember he did the voice of the judge at a pet show in The Addams Family (1992-93) short "Pet Show Thing".