I didn't get a photo of it before it was fitted into the step.

The curved "palm" is 50mm x 5mm flat bar. I curved it while it was still 500mm long, to get the leverage round a bit of heavy pipe as a mandrel, to the size of the mast, all while it was in the vice.
I tapered the edges of the palm to fit the internal curve of mast step. as you can see.
The palm has a 6.5mm hole drilled through it and then it's countersunk from the mast side with a 9.5mm drill to half it's thickness.
I then machined the 1/2" threaded rod (that's what I had on hand) in the lathe, down to 6mm diameter, for a length of 6mm along the thread.
I fitted the "palm" over it, which is a loose fit and gently peened the edges of the 6mm stub with a small ball peened engineers hammer, till it was well retained but still had full movement. I then just dusted a fraction off the "domed 6mm stub" that was left to flatten it with the grinder, so it easily cleared the mast and would not damage it.
To fit it into the step I kept trimming (lots of times) the threaded rod till I could just get it to start threading into the welded on nut from the inside of the step.
This was
all before the step was welded to the chassis/ steering head.
I gave the thread and pivot on the palm a good coating of "neverseize" before fitting it.
I covered the exposed threads with insulation tape while I painted it to keep paint off the threads.
It will be trimmed for length to get clearance for the tyre if needed.
This photo shows the mast step tacked onto the chassis/steering head below, hence the light coming through from underneath.
It's a single still, taken from the video off the GoPro and cropped, so sorry bout the quality.
Hope this helps you.