The problem with the Elder is the design of the rear of the fuselage. With just the uprights and cross members used in the rear of the fuselage, it has no resistance to twisting. If you can jig up the fuselage to square, all you have to do is add diagonal bracing, which is what they did 100 years ago when they built full sized airplanes in this manner. Use thin carbon fiber pultruded rods, which have the strength and will look like the the cables used in the real airplane. Once they are epoxied into place in an "x" pattern in each square bay of the tail boom, the fuselage will be locked into the shape you jig it at.