A999 vs A727 mounting points

Mounting points (engine/trans. crossmember) are identical. Output splines & overall length differ, so you'll need a different slip yoke and driveshaft length. Speedo cable/drive will bolt up, linkage may need tweeking, but should work. Shift selector arm on trans may need to be changed depending on the effective arm length (shaft opening to linkage hole distance) to get your column indicator to register correctly. Torque convertor, naturally, is different.