That is a BIG trailer.
Being respectful of your story line, at the least a 70's 1 ton.
Considerations to your story though - why would someone that has such a nice trailer (that costs a bunch of money) be restoring/rebuilding an old derelict truck? Based on the very limited information about the story I am inclined to suggest a more vintage/size appropriate trailer.
I think you could go a bit bigger trailer than Johns suggestion above, especially with the newer Ford.
https://i.redd.it/f4ake4m7hyo71.jpg
