Looks like my swing arm will be here Friday. I can work around the chain and brake stay issues but I think shock placement might be a show stopper.
Been comparing the different ones through the production lines.
Your correct on the frame tubes sounding thicker. According to a book I just received and digging into, the tube wall thickness of your Z1B is 1.8mm and the next gen A4 was built out of 2.3mm wall tubing. Not sure if they were increased again after the 1977 Kz900 A5. Id assume the swing arm was increased in a similar way.