In answer to your question re: the change in voices, Dustin Hoffman was the original voice of the father. (That's back when I first saw the program.) However, his contract only covered the original airing, not repeats. So, Ringo was brought in to do the voice for later showings. Even later (and I assume this was a matter of rights issues), Alan Thicke recorded it the part. I guess Ringo's voice track was the only one the distributors could use (i.e. could afford).
It is an unusual, but well-made story. One of these days I'll have to check out the book.