KVM Progress Update: I've managed to determine what each pin of the original micro-controller, erm, controlled. I'm now in the process of tracking down what each (section) of those ICs is responsible for.
Oddly enough, the mouse ran through the uC, not just the keyboard. Probably because of REASONS in operation of PS/2 that I'm not aware of.
Not that I care. I just want to know what components are responsible for the entirety of the VGA signal so I can switch the _whole thing_.