Hi David, how is your project progressing? I have some ideas that might help you, but I need a little more information. Is this a personal project or one that you've contracted? Do you have a scheduled completion date when you have to have the job completed or no rush? Do you have a budget cap? It looks like the job scope is small, but a little complicated. You might consider hiring a earth moving service with a track hoe. If the job is personal and you're trying to economize, then you might consider a variation on a logging cable yarder with some sort of bottom dump trolley like this:Click image for larger version. 

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That might get a little pricey, but you could make it where it moves side to side. You could use a cable winch to move the trolley along the cable.

Just some quick thoughts. Good luck!