jb:
1) W123 is a chassis designation, not an engine designation. Hence, there is no such thing as a "W123 Cylinder Head".
2) Over the years the W123 was produced with eight different basic engine designations, and many variations of those basic designations.
3) Your inquiry seems to be for a part # for a specific variation of OM617 (engine) cylinder head. The number in the pic is a casting number. The cylinder head does not bear a part #.