If it's a 1950's fridge there should be no cooling lines in the walls so you don't need to warry about that. My only concern would be for the insulation. But, here is a thought for you. Why not use the tall slim 1/4 kegs instead of a half barrel?
Semper Fi,
The Gunns
"Beer is proof that god loves us and wants us to be happy" - Benjamin Franklin
Im a
MicroMatic Beer Fanatic! Are you?