There was chit chat that when Max Baer played Jethrine (Jethro's sister) on the Beverly Hillbillies that Baer's real sister briefly did a few shots on camera and helped him out. Another example maybe of somebody actually playing somebody else's role. Also, many are not convinced to this day that Frederic played 'Mr. Hyde' in the early 30's film 'Dr. Jeckyll and Mr. Hyde' as he seemed too unidentifiable as Hyde. Back to the great Beverlee. I further stress that some of the parts she supposedly played (like on 'Cannon') were cheap, cheesy roles like wearing a real fake-looking dark wig. Parts much better played by a stand-in/imposter.

I add this. When I was younger I was fascinated with the idea of doubles used for film and political purposes. Well, I learned that before Iraqi mass-murderer Saddam Hussein's government was toppled by Pres. Bush in 2003 he (Saddam) used many doubles to be safe. It seems very much also that Beverlee McKinsey or her agent was sending out a play body double or a soap opera stand-in to do her film and prime time roles. I will say this about Beverlee's prime time and movie parts too (quoting Sundance in 'Butch Cassidy and the Sundance Kid')--"Whoever it is it sure the hell is somebody"!

This lady looks every lady from Connie Stevens ('Mod Squad') to Nancy Kovak ("Hawaii Five-0'). I have probably just fooled you big. You most likely now believe Connie Stevens guested on 'Mod Squad' (she did not --would she have been miscast if she had). But on MS was Beverly McKinsie (or stand-in) looking great as she looked much like Miss. Stevens when she did her first appearance on the show. Nancy Kovak was on Hawaii Five-O in the first season. But on the show's second season McKinsie (or her stand-in) guested also looking great resembling Miss. Kovak. In fact, I wonder if the original Hawaii Five-0 actors thought she was Nancy just back among them again and using another name and make-up job. See why it is doubtful McKinsey was just one woman?

Well, Saddam had doubles all right. I used to call it the Saddam Hussein factory.

More on topic. Actor Maximillan Schell could not fully film the mini-series Peter The Great in the 1980's So for a while Peter becomes seen only in very dim light to disguise the double-actor aspect. There is a clear case of using a double and billing it as a different actor (though not a total case of it).

Back to Beverlee McKinsey. Some would say--why would she want to use doubles? Unsure but maybe her boyfriend thought she would fall for some of those male actors women used to have crushes on like Mike Connors so they sent a lookalike. In the case of Mannix not an extremely good acting alike. A highly modest and mild actress but, however, she still made very pleasant viewing. Beverlee was a lady accomplished on Broadway. You hear what sounds like Beverlee's voice but it sounds so dubbed. So maybe it Bev's voice but not face.

I will doubly emphasize that final point. Beverlee McKinsey had two broken marriages in her background by late 1968. She had to raise a son all alone. She personally had a lot to be completely upset about. But even if her heart was not in this Mannix series role it is difficult to imagine her giving such a completely mild performance. How about an angry performance. You expect much from a lullaby of Broadway. A lookalike would explain it.

I thought of another example. And on target as an analogy. Look at the series 'Batman'. Remember those actors in the Dr. Cassandra playing Penguin,Catwoman and the other regularly seen criminals. Those were of course not Burgess Meredith or Julie Newmar etc. etc. Butr they looked them and they were supposed to be those actors. The lady who guest starred on Mannix was certainly supposed to be Beverlee McKinsey. But it wasn't. The 'Batman' lookalikes also sounded like the show's regular actors and perhaps they were actually dubbed as the lookalike for McKinsey probably was. If dubbed voices then the regulars and McKinsey did in a sense appear on both shows each.

Beverlee, as an 'Hawk', is also uncredited in her first 'Mod Squad' appearance. Suspicious.

Something else.

Analogy.

UK actor Richard O'Sullivan, of 'Man about the House', was supposed to be an ad for 'Sunsilk' but when you see the ad at Youtube ( Classic Ads: Sunsilk) you can see it is clearly his younger and taller brother John .

Beverlee McKinsee clearly was not in Mod Squad ep ' A hint of darkness' her lookalike sister Wanda obviously was.

McKinsey did NOT have a sister & she is listed as appearing in that episode as Claudine Ensign. She was also in another episode as the character Evelyn Ellis.

https://www.imdb.com/title/tt0650039/fullcredits/?ref_=tt_ql_cl

https://www.imdb.com/title/tt0650053/?ref_=nm_flmg_act_10

Richard O'Sullivan did NOT have a brother!

She and also beautiful actress Marj Dusay played the same character on 'Guiding Light' and were in the same season of Hawaii Five-0. No theory they are the same lady.

Update:

I have had the very good fortune to read an old interview Beverlee McKinsey gave in 1991 describing her time on Hawaii Five-0 in 1969. It was right after she did a guest appearance on Mod Squad.She had not watched the show before she landed a part on it ( she auditioned for the role among many other ladies). She was impressed with it once she did tune in. Beverlee described how the director of the ep didn't think she drove a car fast enough. How Jack Lord was very nice to her. She stated she had made pictures of herself with Jack still after all those years. ( She did not say this next part but it is a very safe bet to presume Jack Lord had his arm around her in some of these photos!)