it IS a Sani-7!
Notice how the trim is a dark tan, and the rubber bag topper only states 'Sanitronic'. This came between the 561 (last of the 500 series in 1961) and the 1964 Dual-Sanitronic 50. Those Sani-7's had the most interesting trim, they varied from a light fan to an almost bronze color! Your example appears to be one of the bronze models. The main difference between the Sani-7 and the Dual-Sanitronic 50 is the variations in tan, and of course, the lighted headlamp lens. However, the lighted lens was ONLY seen on the 1964 introduction model of the Dual-Sanitronic 50, likely to celebrate the 50th anniversary of our beloved KIRBY! If you can get the serial number, vacuumland's serial-number-guru, Ben Edge, can tell you a manufacture date in a heartbeat!
The HOOVER is also nice, but be careful with the brush-roll, they're impossible to find now! Someone should really produce a line of replacement brushes!
-Alex.