I think that one reason Jim designed the diamond stab was for the ease of construction. He could build the stab flat on the bench. Jim used saddle jigs for his wings and stabs. I just got through designing and building a symetrical stab for my Bobcat. I used a saddle jig to build it. While not to difficult to make a saddle jig, it does take time and building a stab flat on the bench is easier.
Jim test flew my first R/C airplane, a Guillows Vanguard. It crashed! Not Jim's fault, though. I was a 13 year old kid and I used a hand drill to wind the rubber on my Babcock escapement. No, not a electrical hand drill but the old wind by hand type. However, I didn't know that they were geared 5/1. The instruction said to put 100 turns on the rubber. Well, being geared 5/1, I put 500 turns in and the escapement locked hard over as soon as the airplane left the person's hand who was hand launching it. My beautiful(to me) Vanguard was in a bunch of pieces on the asphalt. Learned a lesson, though!
Frank