RE: CMP Beaver conversion
The front of the firewall needs to be flush with the front of the fuselage. Since I will be using 1/4 inch plywood to build it, I cut the original firewall 1/4 of an inch inside the front of the fuselage.
To keep the new firewall in place, I glued inside the remaining firewall four pieces of 1/8 inch plywood. Tabs were cut on these pieces to hold the firewall in place.
Triangle stock was used to reinforce the whole structure.