Most 8K axles I've seen have 17.5" wheels/tires.
What size are the 16 inch load range F tires on your trailer? The 8K axles usually have 5/8" wheel studs, is that what you have?
I think you did good, maybe saved close to $2K versus new Kaufman. Good luck with it. I am looking for similar, either gooseneck or bumper pull.