Today I finally discovered that the reason I hadn't been able to put two and two together is that the front end of the camera had been rebuilt by SK Grimes, a high-end camera machine shop. The custom work had been designed specifically for a SA 90/5.6 XL. Though I tried a SA 90/5.6 MC that did not work, the slightly different shape of the cone on the rear lens allows the XL to operate. Though I'm happy to have the problem solved, what I originally thought was as simple as mounting up my trusty Fuji 90/8, has now turned into a punt or provide some stimulus money to someone via a purchase of a 90 XL at somewhere around 1000+. Anyways, thanks again to all for your input. I know a lot more than I did previously.