Paul,
I think if you look close that you'll agree that the wing bolt holding the panel on the tube either backed out or was never installed. Had it been, there would be damage to that location on either the wing or the fuse from the failure of the panel - there is none in either position. I think the wing simply slid off the tube and failed when it rotated uncontrollably.
I'm flying a ZDZ 80 Super on standard mufflers. Answers to your questions (well, answers that I have anyway - not all of them):
1. I'll measure.
2. Running mufflers, but I believe the can tunnel is set up for the MTW 110. The manual is available online.
http://www.aero-works.net/upload/manual/75cc_yak.pdf . Better yet, give Rocco or Kim a call.
3. Running mufflers.
4. Pull/pull rudder. Plenty of room for a good CG moving components with the muffler setup. You'll add close to a pound ahead of the CG with a can, so push/pull might be a better option. I'd recommend making that decision with the airplane sitting in front of you.
Scott