I took the firewall and floor stiffeners and gussets out of the fuselage and updrilled them on the bench to avoid making any ugly holes by doing it leaning over the fuselage side. It all went well, but deburring inside the stiffener tubes was a bear, even with a Burr-Away backside deburr tool. The burrs were large and just did not want to break free.
I also added seven rivet holes to the top of the overlapping gussets. The end holes are close enough to the stiffeners that the CCP-42 rivets interfere with the stiffeners. I went ahead and pulled the rivets, and the pulled shanks on the backside of the gussets were shortened enough to remove the interference.
