iMac conversion

I've got 2 iMacs, one slotload, one trayload, and both monitors are dead. I was thinking of converting them into set-top boxes, but the power connector is ATX in style, but not the same size. Does anyone have a pinout of this, or have they done this before?
I really don't want to spend $399 for an iRack and don't want to purchase instructions, unless I have no other options.

Has anyone done an iMac mod? Perhaps moved it to a desktop case, or something similar?