After all my concern about how to establish the three different flange angles during the time I was shaping the form block, I confirmed today that other builders on the list were so right. It is completely a non-issue. Without chamfering any of the form block sides, I was able to tweak the flange angles in less than 30 minutes using my tweaking pliers. My biggest concern in putting a pre-drilled firewall blank into a homemade form block was that the pre-established rivet lines were set, and there would be no way to correct if the whole blank was skewed during the forming process. The real check, as called for in the photo guide, is to put the firewall top stiffener in place temporarily and check for level. I did and it was spot on! Whew.
