seems like a mystery to a lot of people...just in my few minutes of searching 'unity light mount' i found thread after thread of guys trying to come up with a way around the lack of any kind of tab or clevis on the bucket.
Here's my solution...
Lathe'd up a 1" delrin bar into a ball end with a ground HSS form tool then drilled a .375" hole through the center and tapped for 3/8-16.
milled the some flats and cross drilled a hole for a 1/4-20 retaining bolt.
made up a little tab with an angled bottom (to match angle of forks) and spray bombed it.
fully adjustable and the perfect balance or form/function...just like this old light.