Another interesting clue to the date of the Eureka Dial-A-Na
At some point in the 1970's (maybe 1976), Eureka added cooling vent slots to the top of the motor hood. The upright in this pic has no vents, which also makes me think that it is from the early 1970's. The toggle foot switch seems odd - by 1976, the foot switches on the cheaper Eureka uprights were usually plain on-off push buttons, like those found hiding under their canisters' power "pedals". Another clue is the black printed graphic on the bag. By 1974, Eureka was gluing a plastic logo sign onto the bags, not printing on the bag material like in the 1960's.
Though the presence of a Disturbulator agitator can also be a clue for the date of manufacture, this could have been replaced over the years. But if you see an old 1960's bristles-only Disturbulator under the hood, I would date this machine to maybe 1972. I don't think Eureka was allowed to add beater bars by Hoover until 1974.