I am wondering if the 2.0 GHz and 2.3 GHz dual core PowerMac G5's use the same motherboard as the 2.5 GHz quad core PowerMac G5 (which featured two dual core PPC chips). Does anyone know? Is it possible the the 2.0 and 2.3 GHz machines use the same motherboard as the 2.5 GHz machine, simply with one CPU slot empty?

If this is the case, is is perhaps possible to upgrade a 2.3 GHz dual core PowerMac G5 to a 2.5 GHz quad core PowerMac G5?