I've swapped heads on lots of barbies but never tried it with Ken, because of his neck. I already had the Divergent and Hunger Games guys, so I knew I could use their articulated bodies, but I wasn't ready to take the chance until two months ago. After confirming that Finnick's skin tone matched Ken's, I got another Finnick. I didn't build up the courage to do the swap until last week, though.
Finnick is now wearing Ken's body. His head is loose, but Ken's head sits firmly and doesn't move up and down. He is taller.
"Hello!"
I'm happy with him. I wish more articulated bodies were available in other skin tones.