I cut the hole for the slip ring tonight.
Started off by marking the center lines and then using a hole cutter to score the 7/8″ outline where the slip ring body would sit.
I then marked off and drilled holes where the slot would go for the cable plug to pass through
I used a Dremel and a hand saw to join the holes up
You can still just see the outline of the circle I’d marked
I then took a file and made the small circle notches either side of the slot to accommodate the slip ring
Testing that ring slip ring fit and that the plug will pass through
Top view of the slip ring secured in place
Now to solder up the connectors