It's been rumoured that the JZA70 ECU is in fact slightly different to the JZX81 ECU... can anyone confirm or deny this rumour with facts rather than hearsay?

As far as i have unstood the situation to be is that the two ECU's are the same but just have different part numbers and thus Toyota sees them as different. But i know a couple of people believe that theres a physical difference that requires slightly different wiring.