As some have already noted, Songbird I was a Cessna T-50, the Bamboo Bomber trainer from WWII.
Songbird II was a Cessna 310B, S/N 35548, N5348A.
Songbird III was a Cessna 310D, S/N 39117, N6817T.
As far as we know, there were no Barons flown by Sky in the series. The swept tail of the 310D might be confusing some people.
Kirby Grant, the actor who played Sky, was later the official spokesman for Sea World in Orlando, Florida. He was killed in an automobile accident while driving to see a Space Shuttle launch in 1985. BTW - He was turned down for military service because he was color blind and never had a pilot's license.
You can still buy videotapes of the episodes. There is one internet site that sells these and also episodes of the Desilu "Whirlybirds" series and tons of old westerns.
Anyway - flying the 310 is a hoot. It's roomy and fast. Owning one is not so much fun. The engines are packed into tight nacelles and the landing gear is very fragile. Nose gear collapses are common, requiring both engines to be torn down and inspected. Yikes! 
Former 310 owner and Twin Cessna Club member,
Ron King