George,
Put the glue on the triangle side. I used 5 min. epoxy yery liberlly around the top, bottom, sides, all over the triangle stock, and then used a paint brush and "painted" the entire back of the firewall. I had read some threads saying members had their firewalls come loose while taxing and engines floping off on the ground, I checked mine out and to my shock, I could see daylight all across the bottom of the firewall where it meets the bottom wood.(take the tank out and hold the plane up to the light)Too much is just enough. It shouldn't affect the balance, but recheck it anyway. Also, don't forget to check the axial balance.(hold the spinner and fuse backby the tail wheel mount.)