The stop/run motor assembly doesn't have to be a genuine Isuzu part. Suitable motor assemblies are used on many diesel trucks.
Alternatively diesel stop solenoids from ebay can be used, but require a simple mounting bracket to made, and possibly modifying the stop/run lever on the injection pump to suit the stroke of the solenoid. These type are common on all manner of stationary diesel engines. The following pic shows a generic solenoid mounted on the IP ('AD' pump is a little different to our 'A' pump) of an Isuzu 4HE1 engine.
wonted thermostat housing for isuzu 4db1t that came out of npr Isuzu truck top and bottom for 957923 engine number. I know my top one is modiffied as its in a f250 4x4 ambulance that use to be 351 Windsor I am located in Australia Qld