The final step before riveting the firewall is to countersink all of the parts that rivet to the back of the firewall (to accept the dimples).
This was a simple enough task, just lots of countersinks.
I also got started on the forward fuselage ribs (the front of the tunnel). Most of the holes were final sized on these parts but I had to final size the powder coated nose gear tension fittings.
The only other holes that needed final sized were the nutplate screw holes. I upsized these #19.