That is some kind of spare tire carrier. Do you suppose from the bright fasteners on the hubs that it used a spare wheel that bolted on and off at the hub like Rambler did for a while?
There were aftermarket wheels that were demountable at the hub from various manufacturers.
Check out this these threads - there's a nice photo of a similar wheel carrier in the first thread and examples of demountable at the hub wheels.
A beer for Lizzie. Now that's what I call happy motoring!