I used the countersink tool to countersink the rivet holes in the doubler .007" deeper than flush for the firewall dimples. I dimpled the firewall using the close quarters dies and a rivet puller. I made a wood mock up of the connection between the two contactors to get the dimensions correct. It ended up a little longer than what the plans specified. Used the mockup to make a single connector from copper bar 0.125" thick vs the two bars 0.063" thick called out in the plans.
