Here are a couple more pic's of the brackets; doubtful that they'll help in clarifying what they are, but they are here anyway...
With the big nut and washer removed from the bottom
Here shows the bolts with the wingnut do come out, and a better shot of the copper washer.
And here is a different view of the upper bracket on the cab top
With the big nut and washer removed from the bottom
Here shows the bolts with the wingnut do come out, and a better shot of the copper washer.
And here is a different view of the upper bracket on the cab top
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