This squeal, especially if it happens as you start up can be down to a slightly loose belt. You can also end up with the belt and pullies glazed which makes the problem worse. I had this problem when I used a notched type belt, used because I had it, but back to normal with a correctly tensioned standard belt.
All other comments so far are good. The bracket must have the rubber isolation grommets to stop poor brush contact due to dynamo vibration. Not needed for alternators.