Completed the firewall, back riveted all AD4 rivets. The rivets nearest the inside corners of the F-601J angle (they go thru the F-601N stiffeners) "ride" on the extrusion fillet. It was difficult to get textbook shop heads to form. Not clear to me that refabricating the part will result in a line of rivet hole far enough from the inside corner to have enough real estate to form a good shop head.
