What is this DIP20 microcontroller?
The only one I could find was PIC16C717/770/771 but old Microchip microcontrollers have the power pins in the middle, you might find other processors as well. 

Pin 6 is not really a GPIO, for the above series it's an analog ground, I see a decoupling capacitor in your pictures.

Also it looks like the xtal is placed on the secondary oscillator.