Looks pretty familiar
This looks very familiar. My air cleaner cover looked very similar. I replaced the filter element and cleaned the housing with some solvent. I believe that the 'gunk' pictured in your photos are both 'dust' from the breakdown of the sponge in the filter element, and adhesive used by the manufacturer (on the metal screen) to adhere the foam to the screen. Nice to know that much of your sponge filter element probably went through your diesel before the previous owner tore it out, now allowing all sorts of even bigger particles to go through the motor. My engine ran, but I pulled the injectors and had them rebuilt. The company that serviced them remarked that they were surprised that the engine started at all, the injectors were so filthy. Even still, my engine only seemed to banging on 2 of three cylinders, which I discovered when I had to bleed the injector lines. After rebuilding my injector pump and adjusting the governor, my engine now runs perfectly. There's another post where I discuss a subsequent upgrade to my exhaust mixing elbow, after it failed at (of course) an inconvenient time.
Ah, the joys of rehabilitating an old diesel!!