Whippoorwill, You mention that you would have recognized it if it had been done by "the Kingstons". Is it possible that you may have missed one? There was a song written by John Stuart which sounded very "not Kingston Trio". It appeared on an album along with "Last Night I Had The Strangest Dream", and, "These Seven Men". But I'll be damned if I can think of what it was called. It starteded and ended with:
"When you sit and wonder 'bout things that have gone wrong, Then I think you'll understand where our friend has gone..."
These may not be the actual words, but I think they are close.