I've never heard the 91s, but I do have 92s, and the 91s bookshelf twin, the 58S speakers. And I agree with David, that they're a great find, and I'm sure they're wonderful.
Nice locating a recapped pair too. Plus, I wouldn't worry too much about the original 100uF electrolytic capacitor. It's a Unicon brand cap, and they tended to last much longer that some other brands that AR used back then. A Japanese manufactured capacitor, that sounds very good as well.