Metal-base Sanitaire F&Gs are definitely rare
I have an early 70s Sanitaire 643, which is very rare. You wouldn't know it because it resembles the newer Sanitaires from 10-20 feet away. But the main difference between this and the newer Sanitaires is the fact that the 643 harkened back to a time when Eureka-Williams was using cast-aluminum bases for their machines, while the newer (1976?-current) use plastic bases.
I'm guessing the reason why the metal-base Sanitaires are rare (or domestic Eurekas of same vintage) is because of the brushroll. The brushroll on an older, metal-base F&G must be square-ended, which is NLA and has been for some time. I remember searching the ends of the earth for a square-end VGI or II after I got my 643. I did end up getting a NOS VG1, but not easily. The casting of the base does not allow for a hex-end retrofit. So when these started to need brushrolls, I'm sure they got tossed. Otherwise, it seems to be durable, probably more so than the current plastic-base/Quick Kleen machines due to the cast aluminum base.
The motor footprint on the first Sanitaire commercial uprights are exactly the same as a modern Sanitaire, or any Eureka F&G upright for that matter. So if the motor burned out on these, at least that was a replaceable part, though you'd be putting in a 5 or 7 amp instead of a 3.35 amp.
Other than the brushroll, there isn't much else on this machine that wouldn't be compatible with the newer machines. Bags are swappable between old and new. The cord hooks are welded onto the handle, so you don't have to worry about flimsy plastic cord hooks fracturing and breaking.
