Q:
A: No, they are completely different units and even if the wiring plugs match, you will never get it to work. Besides the BSI cannot be recoded to another engine ECU once it has been matched. So if it is a second hand BSI you will need to swap the engine ECU which will not work with your engine, and if it is a new BSI it will simply never recognise your engine, or dash panel, or airbag ecu. Further, a 55 reg BSI is a CAN-CAN interface and an s-reg 206 will be a very early VAN-CAN interface, so even the network protocols are totally different, including their bit-rate. Even before you asked this question you obviously don't know enough about what would be involved to accomplish this even if the BSI could work!