There has been other threads with more discussion you may benefit from, do a search for plywood lift, panel lift, ect on this forum and you should find something.
The one flaw with your drawing is, i think, you need to have your post and your swivel point in the center other wise you are still fighting the weight of the panel in trying to get it to a horizontal position.
Also i would check out something like a drywall lift:
http://www.rakuten.com/prod/drywall-...FRFnOgod63oAYQ
The post is in the center, the platform pivots in the center and you can raise or lower it according to the varied heights of your truck or bot bed, ect.
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