Pat,
I'm sorry but I don't have the specific info you're looking for. However, years ago (back in the late seventies/early eighties) my brother-in-law had the same motor you did. The device he used didn't have metal plates, but rather two large suction cups connected by a "U" shaped piece of metal, which pushed the suction cups towards each other. One of the cups had a hose connection on it. I don't think it was specifically designed for the OMC but rather was a generic design. I don't think you should have too much trouble locating one. Try Overton's (you'll get a discount as a RBO member), Boatfix.com or some of the other online stores.
There's another thread on the site looking for the oldest Rinker. So far, you may be it. Search the site for the thread, post some pictures, and maybe Talon will send you some swag!

Oh, and welcome to the site!