I got a reply from camerons regarding the B12.
Hi Stuart,
The last six digits of the Alpina B12 chassis number are B57526.
All right hand drive 850 B12 Alpina's (5/6 produced) were built at Sytner Nottingham and I have all the supporting paperwork. Only left hand drive models were converted at the Alpina factory.
Please feel free to call me on 01225 892244 should you want to discuss this car in more detail.
In the mean time many thanks for your inquiry.
Ian Cameron