I did a removal of an old firewall pad on a Euro 69. The pad was still in presentable condition, and I used a small putty knife to slowly and carefully peel the old pad off. It had a small layer of foam insulation that just sort of disintegrated as I used the putty knife. Once the pad was off, there was not really very much material left on the metal. I used a scouring pad and steel wool to remove the small amount remaining. Then it was some smooth sanding and a spray of primer, and several coats of paint, and we were good to go.
I was able to get the entire pad off, pretty much intact, and then painted it with a matte high temperature paint, and we re-installed it.