Datasheet report "100% backward compatibility with previous Flexcan version".
I think this is not true by a software point of view.
See for example MC56F8323 flexcan module.
Message structure buffer are very different (same bits but in different position).
Registers like FCMAXMB (maximum message buffer) are not present in the Kinetis Flexcan module because are included in other 32 bit-register like CANx_MCR (lower 7 byte).
And so on.