The late Peter Fernandez told me that the worst kept secret about this movie was that he did the voice of Alakazam, not Frankie Avalon, who just sang the songs. I thought that was unfair, but Peter didn't seem to mind. I believe he adapted the script as well, but I need to check my old article I did about the movie for G-fan all those years ago and see what I wrote. The dialog sure sounds like his writing, with his puns and clever asides. Of course, as a kid seeing this on television several times growing up, we never knew it was Japanese, just that it was a fun cartoon movie with some good music and great animation. That's where our knowledge about it ended.
We didn't know it was part of a long Asian tradition of movies about the Monkey King, since the adaption completely negated that.