That port nupoile had you uncover looks to me like it should be where the keyboard plugs in (with a 5 Pin DIN) but it wouldn't make sense to run power that that connector. Can you tell where those wires run? Other than that I don't see any place a keyboard would plug in.
That Goldstar Prime 2 looks like a standard ISA multi IO card. It handles the hard drive, floppy, serial, parallel, and joystick/midi ports. Before everything was put on-board that was what most systems had.
the keyboard plugs in to the side of it, not the one I uncovered, the wires from the part I uncovered goes to the power supply, and the "Giant blue capacitor thing"