OK, so my McCauley research didn't end up going anywhere. That still doesn't mean I can't show off some more of his stuff.

Here we have the cover of another Imaginative Tales from 1955 that illustrates "Mr. Margate's Mermaid," a sexy and playful image.

Here's how one web site describes the story ...   Man hired as custodian by occultist falls in love with mermaid staying there. However most of the characters get switched with a male centaur ending up in the mermaid's body.

... what's odd is I found this reference on a web site listing stories of gender switches.
I also found an odd reference here, which is a massive listing of centaur names and their sources. 
Boy, the web sure is a weird place.