While I'm welding up fittings on the upper fuselage, I decided to try another location for the inertia reels. I was going to mount them on the aft cross tube, but that gave me little scope for the Y harness. (see entry for 3/25/14).
I made a quick jig out of angle and a steel tab and moved the location back about 10 inches. I put in a seat, seat cushion and tried out the reel. It actually worked much better than I thought. The Y portion of the seat belt was out of the reel (working portion) and leaning forward I didn't experience any quick lock-up of the reel like doing it by hand or my previous attempt. The setup isn't perfect, but certainly functional and the angle to the torso is much, much better in case of a mishap per AC21-34.