Ridge,

I have a 1980 GD300 Cabriolet. Not so sure if the cams are different from the car version motor, but the injectors are definitely different. Many G diesel owners have tried replacing worn injectors with injectors for a 300D car motor of the same year as their trucks, only to find that their trucks would run extremely rough. The spray volume is unique for the GD300 injectors. In turn, your motor has a different torque curve than the normal car motor. Makes sense since even a cabriolet G tips the scale at 5,000 lbs!!
If you raced a stock 300D I am pretty sure your car would get off of the line quicker and stay ahead the whole way.
Where did you find that motor anyway? Pretty rare find. Does it still have the 'megahorn' intake with blockage indicator on it?

Regards,

Steven