About that 560...
I have a Kirby 561 so I may be able to answer a few questions for you as they are very similar machines. The 560 you saw was made in 1960. As far as the bag is concerned it is a cloth only setup. You don't change anything when it gets full. You simply shake it out and place the vacuum over a piece of newspaper. Then you open a little door on the bottom of the bag called the "emptor" and the dirt will fall onto the paper. Just do this a few times, you can even rub the sides of the bag to get more dirt out and it will be good to go. All of the older styles of vacuums had cloth bags with no "disposable" paper bag inside. There were a few exceptions to this rule but the Kirby brand in particular was a late adopter of the paper bag technology.
As far as how these machines are built. In a word, amazing. They really are tanks. The only maintenance they need is to occasionally grease the bearings (not impossible or hard if you are mechanically inclined, I did it), and also check the motor commutator brushes to make sure that they aren't too short to run right. In short, if you can plug it in and it runs right and doesn't sound like the bearings are howling you should be fine. Also note that the fans can be destroyed by vacuuming up hard objects like coins and things like that. Make sure to never vacuum up hard objects like that.
I am really impressed with my 561, it really does a great job every week cleaning my whole house. Oh, and you can get almost any parts for these old Kirby's still. Kirby still caries stuff like brush rolls, hoses, and such. A new brush roll made my Kirby work much better on carpets. It really works the nap up and brings the color out on my large rugs.