I don't know how you would find the year or model of that trailer. But let me say this, or ask this. Do you plan on putting a horse in this trailer?
The outside skin can be sanded, bead blasted, etc., But how's the rest of it?
From your second picture with what appears to be a serial number, possibly on the tongue, I see a lot of deterioration of the metal, ie rust.
What does the under frame look like?
In my years working with metal, what I'm seeing in the pictures is an indication of a whole lot of work.
If the under frame is beginning to rust as bad as the area in the picture, then I'd have to say that you will spend more on refurbishing that trailer than what you could buy a good used one for.
I don't mean to sound negative, but even if you paint the outside and inside, and put new floor boards in, will the floor supports withstand the weight of a horse? I am of course assuming that you intend to use it for hauling horses...
On another note, does it matter who made it or what year it is? Unless you plan on selling it as a particular brand and model???
All I'm saying is just be CAREFUL of how you intend to use that trailer.