I have a Super Redhead and a Goliath Jr. I am reasonably certain that the speakers are the same. The grills on both are 14" X 21" and I am pretty sure they have the same screw hole pattern.
I believe the Redhead has had at least three different grills. The original Redhead had a grill that was like a piece of grating cut to fit and had diamond-shaped holes. The first Supers had grills with a mottled black finish and square holes, and then they switched to the same grill but in a chrome finish.