Discoman, not to quarrel or anything but y'r Keystone uses a round tray that won't fit a Carousel or clone projector.

Back when I traveled to give slide shows I used to tell my hosts that "My slides are in genuine Kodak Carousel trays and that they'd have to rent a genuine Kodak Carousel or Ektagraphic projector. Nothing else will do, and Carousel tray does not mean any old round tray." More often than not when I turned up they'd have a projector like yours -- vertical round tray -- that was completely incompatible with the tray my slides were in. People just don't believe what they're told.

Elmo made Carousel clones, I still have one and more projector lenses than makes sense.