Quite possibly have the RPM sensor in the alternator, such as the engines of Isuzu, Toyota, and Kubota.
Normally these engines carry dense Nippon alternators, Hitachi, Mitsubishi or similar, with the vacuum pump of the servofreno (in case it carries it) behind and the cable of the sensor of the tales of the tapervolutions is connected to a multiple plug that the alternator carries.
I hope I have been helpful.