I think all the boxes were metal with a ground wire in them. I replaced all the outlets in the house as they were stabbed in the back and some wiggled loose and caused issues in the same room. Each one was pulled, hooked around the screw, and reinstalled. As each room was painted, we replaced with all new outlets. I have never went from standard to GFCI. Want the safety of them, but never messed with them other than taking pictures, labeling, and replacing an exact replacement.