I am a "Ford guy" who now has a Freightliner chassis MH, but my last 2 Class Cs were E-series based. Plus all my cars have always been Fords!
What I have found very helpful is the website Official Ford Parts Site | Buy Motorcraft & OEM Ford Parts Online | FordParts.com
You can enter the chassis vin number and browse through the various chassis systems and (for the most part) narrow down exactly what you need. You can even register on the site and set up an account that lets you order the needed parts online and either ship them directly to your home or to your chosen Ford dealer.
Even if you don't purchase it on their site it may get you the Ford part number that another supplier can cross to their part.