"Well he's Irish, he looked like a trad source singer, his voice sounded fairly folky,"
Yes he is, no he didn't, no it didn't, no it doesn't
He looks like a refugee chimney sweep from Mary Poppins and he sounds like an American swing singer from the late forties/early fifties, which fits the tenor of the song perfectly - nothing in any way 'folkie' about it.
I never heard or saw a source singer sounding or looking anything like that - perhaps you might put one up for comparison - otherwise, take your pick from anything Bobby Darin ever did.
Jim Carroll