Chicago Burbs, IL
I don't expect there is a single answer. I'd expect the vertical to be longer than any leg you are working with..and the horizontal wider than any machine.
Lift the end of the pin and wedge this under while you are attaching/removing the legs. Thus the legs dangle.
Although if I was doing this I would steal this design.
https://pinside.com/pinball/forum/topic/show-and-tell-your-diy-homemade-tools/page/2#post-1631922
I like the stability of the box... probably overkill but I only have one lower back, left foot, left knee, left hand... the reason I focus on the left side, is because I'm right handed and that one inevitably would be gripped to the side of the fallen machine wondering "what happened?". 
Best of luck,
faz
Saint John, NB
