Yes, Tom Brett was an Eningeer's Engineer. Remember, in the early 60's both the material and the tools and the hardware were different. He spent a lot of time only putting strength where needed, shaving off every fraction of an ounce he could. Parabolic sheeting, cross-grain, hollow tips, balsa doublers, almost no bulkheads, or short ones, all contribute to lighter weight. Today, I would use 1/32 ply doubler, and build it like a Kaos fuse. Of course, the only straight lines on this are the LE and the hinge lines. He must have loved his french curves. That's why the plane is so visually appealing.

Yea, go back and sand an airfoil into the tail! Takes less than an hour to do, except for the glue drying.