The Mechanical Tach drive mounts on the timing case cover and connects with the Injection Pump Shaft for drive power. From the Cummins Parts Catalog you need;
1 Coupling, Tach Drive 3905306
1 Seal, Rectangular Ring 3903475
1 Adapter, Tach Drive 3903476
1 Drive, Right Angle Tach 3905217
2 Retainer, Tach Drive 3903644
2 Screw, Hex Head Cap 3027685
1 Seal, O Ring 3905218
In the Cummins Parts Catalog, it appears that;
Drive, Tachometer 3905309 is a kit with all of the above parts. But that is not spelled out clearly
Also, it does not state if the drive adapter is a 1:1 ratio or ? You need to check with your Cummins Parts Counter on the Ratio.
Paul