Remove the 460, the rubber engine mounts, and the engine perches (metal brackets). Use the perches and rubber mounts from the donor truck to install the 6.9/7.3. You cannot install the Diesel using the 460 mounts. They are quite different.
You cannot use the C6 that is behind the 460. You need a C6 that was originally bolted to a Diesel. A C6 from a 460 and a C6 from a Diesel have the same bell-housing bolt pattern BUT the Diesel C6 has a large cutout on the bottom of the bellhousing. The 460 C6 does not have this cutout. The cutout is needed with the Diesel in order to access the torque converter bolts. If needed, I can dig out my Diesel C6 and take a picture.
As far as I know, the 7.3 came out in 1988.
Electrical requirements for the Diesel are rather simple. Assuming a 7.3 style glow plug system......the glow plug relay needs its own cable run from the battery positive post to the large power post on the relay. The harness that came with the Diesel only requires one wire to be energized with a wire that is hot when the key is in the run and start positions. The harness will distribute the power to the glow plug controller, the fuel heater, the high idle solenoid, and the fuel injection pump shut off solenoid. If you are good with wiring diagrams, the picture below is all you'll need. The oil gauge will still function. Just connect the oil pressure sending unit wire from the 460 to the Diesel.
You will need to install a second battery (use the parts from the donor truck). Same goes for the large Diesel starter battery cables. You will also need to install a "Water in Fuel" light in the dash. All you really need is an indicator light. If the light comes on, you'll no what it is....after all, you installed it. It doesn't actually need to say "Water in Fuel". You should also tranfer the low vacuum warning light from the donor truck to your truck. Actually, do yourself a favor and just convert to Hydraboost......they are awesome. Ford really screwed up when they did not put Hydraboost on everything heavy duty 3/4 ton and up.
The picture below shows the 7.3 style glow plug system. This is the early 7.3 system with twin 10 ga wires supplying power to the glow plug solenoid. Later systems replaced the twin wires with a single 2 ga cable. If the donor has twin wires, remove them and replace with 2 ga cable. The twin wires were a big problem and could easily set your truck on fire.
Transfer the 460 alternator directly to the Diesel engine leaving the wires just as they are. The alternator gauge will still function.
Also need to transfer the Diesel radiator and associated parts.
If you get a complete donor vehicle, it's doable. Just take your time and switch everything over. Including the small parts (eg. Water in Fuel light) so that it's done correctly.
I was (at one time) going to convert an '88 E350 from a 351W to a 7.3. I researched it heavily and collected 90% of the parts I needed. But thinks in life don't always go as planned and the convertion never happened. I still have all the parts though........I will use them some day for some project. I really like the 6.9/7.3's and can't stand the new trucks. Sooner or later, I'm just going to have to build what I want. Not what Detroit and the EPA tell me I want. Sorry to rant.
Dave