N57d30a vs n57d30b engine block.

[B70]

Hello.
Need a new engine block or my 2011 n57d30b engine.
I tried to find info on what the diffrence is between n57d30a and n57d30b egine blocks.
I red somewhere thet the only diffrence is in the cylinder head on the engine and that the block should be the same.
Can anyone shine a light on this .. if i can use A block and bolt on all my parts form a B engine?