The 7.3 uses a 1/2" head bolt, and the 6.9 uses a 7/16" bolt. The heads of the bolts will be smaller on the 6.9.
Also unless he has changed it, the pump drive gear cover will different on the two. The 7.3 has the tube molded into the top of the cover, with a plastic cap, and the 6.9 has the tube as part of the front cover, with a metal cap.
Also the fuel filter housing on a 7.3 has the heater built into it, and the water drain on the bottom of the filter. The 6.9 uses a seperate water seperator.