...............Set it up in a rotary vice and then scribed the lines for the insert.
Ist cut, after indicating set up for a 120º cut.
2nd cut, rotated 240º for the 2nd cut.
Intervening metal removed and trying the insert for fit, then spotting for the screw hole.
Drilling and then taping for the attachment screw.
Milling off excess material.
The insert in place. Just have to make the top block to secure the insert.
Drilling the tap hole, and then milling the relief for the locking bar.
The locking bar in place, and drilled ant taped for it's retaining screw.