Once the stainless steel firewall was deburred and dimpled it was on to the supporting angles, gussets, spacers, etc. I deburred all of these parts and then layed them out on the firewall to label which parts had to be countersunk and which ones that didn't. Then I pulled out a piece of particle board and drilled / clecoed each firewall part that had #40 holes to the board and countersunk them. This works out great as far as holding each piece and using the holes drilled in the wood as guides for the pilot of the countersinking bit.
Angles, plates, and gussets deburred; Marking for countersinking
