Hi Sam,
What year is your E450?
I ask because shortly after buying our motor home, I replaced our 2007 E350 single CD radio with a six CD version of the same radio only so we could play 6 CDs at a time. I quickly learned Ford changed the main connector in back of the radio around that time. I had bought the wrong radio on Ebay which looked identical in every way (except for the connector socket). After I got the right radio, I sold the wrong one and kept my new-ish single CD unit as a spare.
Here is a picture I took at the time. The two radios on the bottom work with my 2007, one my original single CD, the other my 6-CD. The radio on top is an older model year, maybe a 2005 but not certain of it. It might be older yet. Just make sure your connector will plug into one of these. Also note the white plastic on the radio to the right, the black rubber stem to the left. They are interchangeable pending your E450 mounting requirement.
As others mentioned, you can use the radio from many different Ford vehicles of the same vintage. I would take some pictures of your connector and compare it to the socket on the radio you are considering.
Ron Dittmer
PS: I respect your passion on the tire topic. We will just have to disagree on that one. All is well here on my end.