It looks like a panel removed from a Neve. The only thing I can think of is back in the 70s Neve made some huge custom consoles, for NBC or CBC I think, for their Montreal Olympics coverage. I seem to rememeber it included a number of simple mic sub-mixers, possibly for crowd sounds?
there is not much else to photo. behind the panel the pots and the switches are wired to the transformer. everything else is pretty much missing as it was clearly cut off. There is a wiring tie bar but that is it. from the wiring the pot seems to happen right after the transformer.
All Neve consoles of that era used passive mixing. There is nothing wrong with it if done properly. You can see the care they too to make sure the bus was screened an all four sides.