I would think they have to be nose wheels, as there are no brake attachment points. The only difference between the two halves is the 599 part does not have a hole for the valve stem.
I also wonder if they could have come from a prototype or test aircraft. The serial number on the parts are so low, there are two wheels and four tires that have absolutely no wear, and the guy I bought them from said they were surplused from Wright Patterson many years ago. They did a lot of testing at that base.