For awhile, I had an '85 F800 that I used to help build our road. As expected, it needed some TLC and a few parts while we owned it. Ultimately, I ended up finding the chassis and engine service manuals via eBay. Those were very helpful in terms of diagrams, specs and procedures. The one thing they were essentially useless for, though, was part numbers. In most cases, the parts diagrams only had the "core" part number listed. As you'll find out, Ford utilized both prefixes and suffixes to the part numbers that change with application, time, or general parts evolution. Whenever I needed something, I just copied the page from the manual & took it to the dealer for them to decipher. In some cases, that still means you better know the specific options on your truck so that they can narrow down the application. It was a lot more of a PITA than I would have expected, but given all the build/option variations, just the reality of the situation.
So, beyond basic filters, your best bet is to find a set of manuals. With those in hand you'll be able to tackle most anything other than deciphering what current part number you may need!