Here are some updates and more pictures from the ongoing rebuild.

You can see the cutout to open up the front of the tunnel for a little more airflow. There is approximately an eight of an inch all the way around the cannisters when installed. The mounts do block some of the airflow, but it is about as much as I could get through the front opening. The back mount offers much more space around the cannisters. The sides of the tunnel are 1/8" birch plywood with 1/4" braces on the inside. This connects the rear of the landing gear mount to the rest of the airframe. There are 1/8" braces running from the LG vertical back to the bottom of the fuse and a 3/8" basswood brace down the middle. I am going to screw a 1/8" superlite ply hatch down here so that I can get into the tunnel if needed. The front of the tunnel sides under the LG plate are going to get another brace, but otherwise will be fairly open. I am thinking of putting scoops in that extend just a bit past the cowl to fee fresh air into the tunnel. You can see the air exit vent framework at the rear of the tunnel. It will exist the bottom of the fuse just behind the rear cockpit/radio bay former. It is a tight fit to get both cannisters in, but they do fit.