Still searching for a top plate
But in the mean time I found these old brackets that use to encase a fireplace barrier.
So....... it is steel, so...I shall weld it.
I am going to add some 3/4" square tubing 4 feet in height to the top of each bracket. Where a another 3/4" square tube will be a cross bar.
The top of the cross bar will hold a 4' fluorescent light ballast, to hang over the work station.
You can see where I drilled 2 holes at the top of those brackets. That is where I will insert a small bolt and nut so I can fold, raise or lower the light ballast assembly.