Kenny, it's a good thing your Mom was using a Kirby from the 70s - since it had the metal fan, the bag patch was all that needed to be done. If it was a Tradition or later model, you would be needing to change the fan too.
Back a few years ago, I answered a Kijiji ad that said "Free Hoover Windtunnel Canister Vacuum". This was one of the Futura style models, not the Anniversary Edition. Said it was working but needed repair. So, got it home and everything seemed fine....motor running, electric hose working, etc. So figured they were just paranoid and nothing was wrong with it. Vacuumed with it for about 5 minutes, and then the electric hose started smoking and melted into a pile of rubber on my kitchen floor! Needless to say, it went into the dumpster that night.
I figure the owner or a repair shop opened it up, attempted a repair, re-wired the vacuum wrong and that's why they thought the vacuum had gone bad. If it had been wired up correctly, it would likely still be in use.