glueman the authentic way[ that is the way all traditional singers that i have heard[ sam larner harry cox sara makem,fred jordan,ron copper] is to sing them in a natural manner, a natural way to sing is to use both mouth and nose for breathing., it has nothing to do with mannerisms.
trained singers are trained to breathe through their mouth only. by the way those people that would have heard me sing would generally agree that i can hold a room unaccompanied, i have a fairly powerful voice because i sing using my diaphragm
http://www.youtube.com/watch?v=UUoZkOw02uE