Concur with Tiny. I used to haul horses professionally and I wouldn't touch that trailer with anything less than a modern 1.5-ton diesel dually (like a Ford F-450/550 or a Ram 4500/5500. An antique 1/2-ton would require so much upgrade and fabrication/modification as to make the project not realistic.
The trucks you are considering would be better suited for something like this:
2-horse straight load bumper pull.
A somewhat popular project is to take a '50's vintage Cab Over truck and either put the sheet metal on a more modern chassis (like I suggested above) or just upgrade the original one with a modern diesel, transmission and real axle suitable for what you are contemplating for your story.
Something like thisCheck out our Gallery Pages. We have a few like that in here, too, for ideas.
Thanks for stopping by!
A writer .... Cool!!!

John (retired PJ)