Don, I'm not sure that Ronnie Browne's "Jock o' Hazeldean" is the ideal example of extended vocal range.

The Corries play this in C, and it surely isn't difficult for any folk singer to hit the initial C and drop down to the G note on "lady" in the first line.

Personally, I prefer to sing Jock o Hazeldean in D, but I have to confess I chicken out of kicking off with a high D, and sing a B instead. No problems reaching the high D later in the song however.

Works for me ...