Yes, this is true, as my VN is running an EL XR8 3.45 ratio lsd. Was rebuilt by a reputable diff shop. From what i know the reason behind them using Ford ones is the fact that they are usually cheaper, never actually done any research though, so don't quote me on it. I think it is only up to EL that fits, although i have been told the AU centres are also the same?
just be carfull of what center you actuly get because there are three from memory to suit diffrent diff gears i have one doing nothing still got a real strong lsd in it to suit 2.72 to 3.55 ratio
Yes the 2.77:1 carrier is completely different. It can however be used with a 6mm thick spacer ring behind the crown wheel to bring it back to correct alignment but this is not ideal.