Talk to the vehicle inspection authority before attempting work. They may not let you do this unless there is a diesel engine version approved for your specific vehicle/model year. Likely, the revised registration needs to reflect the new diesel engine and you will need to pass the 1997 emission standard. (IM240 test procedure).
The answer depends on how "pre 97" the vehicle is, and what the GVW of the vehicle is, if it is a truck. The answers should all be in the guidelines given in answer #1. Good luck.