I think the age of this Eureka upright can be determined by the many vintage ads for the Roto-Matic canisters you see on eBay. If I remember correctly, the very first RotoMatic advertisements had a small section on the bottom of the ad touting the "Automatic" upright. So if you can date the first red Roto Matics, you've got a date for this upright.
Believe it or not, I think Eureka used the date in the model numbers for their uprights: 250 was around 1950, 260 was around 1960 and 2070 (they added another digit) was around 1970.