That is a Reslo RB ribbon. They came in a variety of formats, the basic ones were 30 Ohms (designed to feed a transformer in a valve pre) but there were 600 Ohm models and, probably John's mic, a 50k high impedance type that could drive a guitar amp. The one in the picture might also have a switch (UGH!)
I have removed the front and back grills for you and smudged them...WHAT a bloody fiddle getting them back on!That and the "acoustic correction" pads interest me. Before I knew of these pads, I wondered how bad the sound would be with the polar pattern. . John singing into the front, and the audience/room-noise coming into the back. Unusual bit of gear.
Audience pickup will be minimized by the felt pad a bit but mainly due to the mics low sensitivity, even the high Z model necessitating very close working ( Google "critical distance in PA work") The front and rear polar diagrams of the RBs are in no way symmetrical!
I have a couple of the STC/Coles famous lip mics . . .