The earliest I found of the feather story was 1896, but I think I found it by accident I wasn't even looking for that, so it may go back way further.  Still, thats still almost 100 years from the purported birth of the cocktail, which is mentioned 200 years before that, by shakespear in Romeo in Juliet "death cocktail". He died in 1616 so we know the term was in use then.  Dont believe me see it for yourself. but what do I know, i'm not expert or even valuable enough to contribute without being reverted.