Tri-stock on the engine side of the firewall won't do any good. The tri-stock needs to be where the firewall connects to the fuselage on the inside of the fuselage. Another thing you can do to strengthen the firewall is to pin the firewall to the fuselage. After you have worked glue into the gaps between the fuselage and firewall you will need install pins. These are actually pieces of wooden dowel, 1/16"-1/8" depending on the size of the firewall. Drill a hole through the fuselage into the firewall. Then put a bit of epoxy into the hole and then drive the dowel in. Then cut the dowel off flush with the fuselage sides. 2-3 on each side of the fuselage will usually do.

Hope this helps

Ken