Hello Phil, This is what I use, Two bits of angle iron, The bottom is slotted, Undo the bottom bolt until it slides
Behind the bolt head, The top has a small plate with two 1/4" bolts that slides in behind, DON'T do the small bolts up tight, Or it will dent the top box, I use some duct tape to save the paint.
Undo the top bolt a small bit.
Tighten the nut on the long stud , Till the top bolt feels loose.
It was in MPH many years ago, By the late Roger Haylett.
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