When I see the words "Wing Span" and "Fuse Length" I take that to mean what it says. I haven't figured it up but I'll bet the wing area wont be 780 sq in. You are correct about using the JR 3421SA's but it would only save a coulple oz and I'm over weight by 1 1/2 lbs.

Specifications

Wing span - 66 in.

Wing area - 780 sq in.

Fuse length - 72 in

Weight - 7¾ - 8½ lbs