Mine (Ford/Sabre 120) is a electric mechanical switch mounted behind the oil filter, it does not look like that part.
Call Bob at American Diesel, bet he can get one to ya http://americandieselcorp.com/
Here is a replacement drive unit for a Packard/Sabre 120 (same) mechanical to electric adapter it you want to also replace the readout.
Lauderdale Speedometer and Compass
Many boats now use the alternator as the tach. drive you may be able to replace the dash tach. unit and wire up the alternator and forget about the older set-up.