I think all Classic IIIs had shake-out bags. My understanding is the first Kirby model to have a filter bag option was the Tradition
That said, I had a similar challenge with a Heritage '84. The bag was filthy when I got it, so I took it off the Emtor and laundered it. I spent about three hours trying to wrestle it back onto the bag, but finally gave up and substituted a plastic mini-emtor from a Heritage II, which took about 15 seconds to install. Now knowing the inside-out technique, I may have to give it another try. I'd like to have the original emtor/fill tube assembly in place so I can use up a small supply of Style 2 bags I have on hand.