I'm having the same trouble you are finding a wiring diagram for this motherboard but thankfully there are ways for us to find the power pins without one.
If you have a multimeter or circuit tester available, the safest way would be to remove pairs of wires at a time (remove in pairs and replace, so that you don't mix them up). Pair will run horizontally, along the length of the header (the bank you described). Then plug your meter into the two removed wires and set to Ohm/resistance measuring. If you hold in the power button and the resistance goes near 0, you've found the power switch! You don't need to worry about wire polarity in the new case as + and - don't affect the power switch.
If you don't have access to a meter (and cannot build a simple one) then the next alternative is a bit riskier, so follow the steps carefully.
With the power cord unplugged, remove one pair of wires from the header. Plug in the power supply and wait 5 seconds for the board to charge. You will need to bridge or "short" the pairs of pins very briefly to find the power pins. This can be accomplished with a metal screwdriver or something similar. The power pins will be next to each other, and not across a gap.
The reason this must be done while the motherboard is in the full 'off' state is that the LED leads may be shorted out otherwise. If the board is off and the LEDs are therefore off, there will be no current to damage the board with.
When wiring up the LEDs in the new case, simple trial and error will guide you. LEDs will only operate when plugged in to their respective + and - ports.
Following the directions above will also prevent you from mistakenly wiring the reset pins to the power button. Please return and let me know how it worked out. -Raj