Back side of a MD and the one for both filters the same closest. Only difference in the other side is the aux filter hole opening size. Real late MD can have a casting that looks the same on the back side but hole sizes are different. Different filter bolts for MD pictured. Both the long shoulder bolts used with both filters the same. Only about a 1/16 size in some hole openings. Fellow could probably make a thin sleeve to work and put a spacer on the original bolt if wanting to put a finial filter in the aux. Casting I have needs a good cleaning and was selling cheep just so someone would get some use from it. Email is open if interested if not thats fine.