Are the cinder blocks sitting on raw ground? If they are you will have to use some sort of bracket between the blocks and the wood. If you didn't you will find the treated wood will rot within a few years.
What you needed was a 3rd container so that you have 3 side-by-side units that would be considered water/weather proof once connected properly.
As Mark points out above, you will need a structural engineer to deal with this. The issue isn't (necessarily) the weight allowance. It is the wood's exposure to moisture through the point-of-contact with the cinder blocks (which leak like a sieve).
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i uploaded some pictures.
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