Hey stang, this is a cool project. Kudos on your work, looks neat and orderly. However, I see a potential design problem on your main beams.
At 2.67 yards, you're gonna have some weight there. I'd be worried about shear in the 2x4 beams right where the bolt is. Anyway, you can just put a 2x4 directly under the beam and nailed to the side of the 4x4 and there is no potential shear issue. That would be 12 pieces per bin. I can exlain it further if you'd like. Those puppies are going to weight 6500+ lbs a piece when full. More if it's raining.