Pardonme if I've posted this in the wrong forum, not a whole lot of space for the old slide projectors anymore. Anyway, looking for the correct slide tray for this 1950's Keystone K511. It is not a carousel. I did find a so-called universal for many brands (keystone being one of them). Wasn't sure if I would have good luck with that or any of the yankee universals.:confused: could use the help thanks!