Go to eTrailer or southwest wheel online. You will be able to get info to determine the bolt circle diameter and center hole diameter.
Do you know that the trailer brakes work?
I recently drove from Breckenridge to Denver. It is a long steep hill.
To be clear, that is a drive where there is great risk of death if you do not have a full size pickup truck or full size SUV as the tow vehicle and reliable, fully functioning, trailer brakes.
Does the trailer currently have brakes? Are the brakes electric or hydraulic surge?
You can purchase a “Trailer Building Kit” from Southwest Wheel for around $1100 delivered. The kit at that price includes:
5200 pound single axel
12” electric brakes
Springs and all hardware to mount springs and axels to the trailer frame
LED lights
Radial tires and wheels. The kit lists 16”. They changed to 15” load rating E tires and wheels at my request.
50 degree coupler and jack. The jack and coupler might not be suitable for your application.
So, if the trailer lacks brakes you will be into the above stuff plus demolition of the existing running gear and installation of the new items.
Or, perhaps the trailer has mobile home brake drums with rim type wheels. Google mobile home wheels and/or mobile home hub drum assembly
Ward