In the craziness of yesterday, some of the rivets need to be redone. drilling the heads off is easy enough. But I am dreading punching them out of such thick material. So... I cut a piece of oak that and fashioned it so that it would support the firewall when I drove the rivets out of the firewall.
This actually turned out to be an incredibly good tool. This gets placed under the firewall assembly and the rivet head gets placed inside the "notch". It then is able to support the area as you punch out the rivet.
I use some oak blocks under the firewall to support the 3 corners that I am not punching the rivets out on.
All done