the ID number of the BMW 6L engine is next to the engine support below of the admission manifold
ex: 206S1XXA 206S2XXA for M50B20,S3 forM52B20
256S1XXA for a M50B25 NV ,S2 for Vanos, S3 for M52B25
286S3 for M52B28
and on the the cylinder head ( next to the temp sensor ) it is the displacement again