I suppose the reported difficulty to meter fuel (and thus engine speed) is more or less inherent to smaller engines for several reasons. First, the smaller size of the metering linkage would make incremental and fine adjustments less precise than their larger counterparts on larger engines. Second, the lower manufacturing costs required for smaller engines probably affect how precise the injector pumps and governor assemblies are designed, built and assembled.
I wonder if modifying the linkages for the governor and throttle would help. I know, it's not technically a throttle function, but throttle is the common term used for everything from gas and diesel engines and even the speed control on electric motors - I refer to the 'go' pedal on my electric golf cart as the throttle, too.
and you basically take away its ability to govern unless it is designed for it
If I understand this statement you are saying that the speed control is direct and there is no governing device between the control cable and the injector, is that correct? I would think that some type of governing feature would almost be a necessity - especially if you are doing something like plowing, tilling, etc. Without some governing feature it would seem that you would be spending your entire day just moving the throttle (fuel control) up and down.
The discussion of these various details regarding the diesel power plants is very interesting and informative. While it does not dampen my interest in transplanting a diesel engine into a GT
it does provide a good idea of the things that need to be addressed and overcome.