Got a couple of firewall passthroughs from Plane Innovations today. Wasted no time in fitting them to the firewall. One is 1", although the cutout in the firewall is only 7/8", as large as I can cut with the bits I have. That's OK, it's enough, and the fitting needs some extra space for the firesleeve. The other fitting is 3/4". The hole I cut was 3/4", but a snap bushing will take up some of that. It might be a bit tight, but I think it will also work. One more firewall task down, now just the control cables to worry about.