As you can see above, before gluing in F3, F4 and F5 (the bottom bulkheads), first put the tailwheel plate in, and then a small piece of balsa at the rear of the fuselage. This rectangular piece was 1 1/2 inches wide. Taking in consideration two 3/8 squares pieces and the 1/8 inch fuselage sides, this put the rear of the fuselage at 2 1/2 inches per the plans.

There were a lot of triangles in the kit. Lay them out by size. They go in front and back of each of the forward three bulheads, and around the engine box. As you can see I took a hole saw and put a few lighening holes in the back area as well.