At http://en.wikipedia.org/wiki/Toyota_H_engine it says Output is 135 hp (101 kW) at 3500 rpm with 231 ft·lbf (312 N·m of torque at 2000 rpm.
This can be substantially increased by increasing boost pressure and fuel supply once an EGT gauge is fitted to ensure the engine is operated with reasonable limits.
Currently my 1987 has 195000 which is just getting started i ha a 2h with 400000. My 12ht runs like new it can sit for months and will start with the flick of a key. I have replaced the water pump after a coolant flush but thats. Never let me down
The HJ60 repair manual I have is vague about tacho wiring. Some trucks used tacho pickup off the alternator winding before the diode plate, via an extra small wire connected into the alternator.The 2H, and presumably 12HT, have a magnetic pickup on the edge of the bell housing over the flywheel on the left hand side. It requires the magnet to be on the flywheel which mine does not have.
To fix a 12V diesel tachometer, first, check the wiring connections for any loose or damaged wires. Ensure the tachometer is receiving power by testing the voltage at the input terminal. If the connections are intact and powered, inspect the sensor or signal source, typically a magnetic pickup or alternator signal, for proper operation. If these components are functioning but the tachometer still doesn't work, it may need calibration or replacement.