No 50 year old was ever a playmate. The oldest playmate was 35. Not sure about cover girls.

Assumng ths was a pose, as opposed to just a picture that accompanied an article, then if she was in her 50s she must have been famous, most likely more famous than her husband the boxer. She could be an actress, perhaps a famous starlet who was born in the 1920s and starred in movies during the 40s or 50s.

Betty Page is one possibility, born in 1923, she's been in playboy many times, but she had no boxer husband that I could find.