Carl Ballantine played Gruber.....
He was an old vaudvillian style act, as a magician.
Not only did he play the purple heart scam, he was always scheming. Very much like our F'in hero.
Another of McHales merry band was Gavin MacLeod who played Joseph 'Happy' Haines
1) I was not familiar with Gruber background, so I started Googling
2) Then you put in your details to Kirkwood, (thanks) so I went to IMDB where I found following:
"In addition to being an actor, Ballantine is an accomplished magician. - show more"
So I clicked Show More
music louder now.... "Trade mark"
"Supposed tricks of magic, which always flop." http://us.imdb.com/name/nm0050535/
http://us.imdb.com/name/nm0050535/bio
So, here finally, is the tie back to the Flip Flop......;)