I am not a engineer or tuner, but a mechanic, and here is my best shot
Giving it more fuel will not neccessarily give you more power, just more smoke. You need to get the engine more air aswell. The 240 engine might not have any more power to give without a better injection pump, bigger valves, more air flow, bigger injectors.
There is a point where a diesel cannot burn fuel faster, and it would take alot of experimenting to find out if the engine is capable of more power (short of a turbo or blower).
On VW 1.6 diesel's you can adjust the "mixture", ie give the engine more fuel at full throttle, but this just results in more smoke, not more acceleration, unless you do something to make the engine breathe better.
So in theory, the 300D injectors might give a cleaner burn (higher pressure resulting in better combustion), but I don't think you will see any improvement in power without other mods.
Some one please correct me...