I think the heavy steel stake is meant for building frames to pour concrete. It's 36 inches long, pointed at one end, and has regularly spaced holes at the top that 3/16 inch (#10) bolts can fit through.
The back plate is made from two electrical junction box covers sandwiched together.
Two U-bolts fit around the bicycle hub without touching it...
and two more U-bolts hold the assembly on the stake while allowing it to swivel freely left and right.
The assembly is loosely held from sliding off by short pieces of PVC pipe above and below, which are bolted to the stake through the existing 3/16 inch holes.
The assembly is held upright by four guylines and four stakes.