Are you using the old 5 pin keyboard connector that preceded the PS/2 connector? WOW!
Let's see: An IBM keyboard plugged into a 5 pin to PS/2 adapter plugged into a PS/2 to USB connector, plugged into the USB port on the back of the computer. Hmmmm... It seems you wouldn't have to worry about air flow behind the system. Plugging in that IBM keyboard will keep it about 4 or 5 inches away from the wall!
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