* Motor Mounts: The 7.3L and 6.9L have different motor mount locations. You'll need motor mounts designed for the 7.3L in an '84 F-350, likely custom-made or from an aftermarket supplier specializing in engine swaps.
* Transmission: The 6.9L likely used a different transmission than a 7.3L Powerstroke. You'll likely need to swap the transmission, driveshaft, and potentially the transfer case, depending on what you choose. This is a major undertaking.
* Wiring Harness: The electrical systems are completely different. You'll need a wiring harness specifically for a 7.3L Power Stroke in that year truck, or undertake a very complex rewiring project.
* Fuel System: The 7.3L Power Stroke has a significantly more complex fuel system than the 6.9L. You'll need all the associated components (fuel tank, lines, pump, filters, etc.).
* Exhaust System: The exhaust system will need to be replaced or significantly modified.
* Cooling System: The 7.3L has different cooling system requirements. You'll likely need a new radiator, hoses, and possibly a different water pump.
* Computer Control: The 7.3L Power Stroke is electronically controlled, requiring a Power Stroke-specific PCM (Powertrain Control Module) and associated sensors.
In short, while the engine *will* fit, the swap is a very major undertaking requiring significant mechanical expertise, specialized parts, and a substantial time investment. It's far from a bolt-on swap. Many people choose to do this swap over several months of evenings and weekends. Consider consulting with experienced diesel mechanics before starting this project.
