I bought the main parts for a Victor V286C a couple of days ago (motherboard and riser/EGA), and - after some minor hacking - it starts up just fine.
I used a multimeter to find the pins of the power connector - using the ISA-slot for reference. It may LOOK at bit like a classic AT-connector, but clearly is not..:

1-3 --> GND
4-5, 9 --> +5V
6 --> -5V
7 --> -12V
8 --> +12V
10 --> Power good

As always, don't take MY word for this, but at least it powers on when I short pins 9 and 10 (for Power Good), and connect pins 3 and 4 to an external 5V source.

I am thinking about about building my own case for it - possibly something like half the original case, without the full power supply and drive bays (in other words the right half when seen from the front) - but with a "simple" 5/12V power supply, a 3.5" floppy and possibly a CF-card for HDD.

One problem, though: I so far has not been able to find any information about the pinouts for the CN11 (power button) and CN12 (keyboard/mouse) pin headers.

I am primarily interested in how the pins of CN12 connect up to the keyboard DIN, since the machine DOES power on when I just add external power - without having to connect anything to CN11.
I have beeped out a few pins for CN12:

2 --> Mouse IC, pin 35
3 --> GND
4 --> Mouse IC, pin 33
9 --> +5V

But no luck apart from this. I have not found (or really actually looked for) much info on the mouse IC (which I don't have)..? Could be an 8255 or something?

Any help would be greatly appreciated!