Here we have a pair of Legendary 16ohm Celestion Green Back, as used by Joe Satriani, Scott Anderson and many more. They has has very little use as after 10 hours or so I took it off a cab of 4 and combined it with Celestion V30. You can wire it in 8 ohm or 16 ohm, stereo or mono. They sometimes match in a 4x12 cab with 2 Celestion V30 or Celestion Lead 80.

Here is the manufacturers description.
The G12M Greenback has evolved over the decades but still retains its essential, sought- after tone.Angus Young has been a Greenback devotee since the early days of AC/DC. This model is voiced with additional broad mid-range attack and restrained top-end to give a forward, punchy attitude to chords and a searing lead tone without fizz.With its well-controlled low-end it can be used singly in low-powered amps, or in multiples for high-power rock heads. It's an ideal speaker to bring drive and definition to modern high gain amps.

General Specifications
Nominal diameter: 12", 305mm
Power rating: 25Wrms
Nominal impedance: Available 8Ω or 16Ω
Sensitivity:98dB
Chassis type: Pressed steel
Voice coil diameter: 1.75", 44.5mm
Voice coil material: Round copper
Magnet type: Ceramic
Magnet weight: 35oz, 0.99kg
Frequency range: 75-5000Hz
Resonance frequency, Fs: 75Hz
DC resistance, Re: Available 6.7Ω or 13.1Ω

Mounting Information
Cut-out diameter: 11.1", 283mm
Diameter: 12.2", 309mm
Magnet structure diameter: 5.9", 150mm
Mounting slot dimensions: 0.31", 7.9mm Ø
Mounting slot PCD: 11.7", 297mm
Number of mounting slots: 4
Overall depth: 5.1", 130mm
Unit weight: 7.9lb, 3.6kg