I'm planning to build a wall block mailbox with the wall blocks that are 3.75" X 7.5" X 11.25". I've worked out the plans that allow for a particular mailbox to fit nicely in a space. However, it occurred to me that the blocks directly above the mailbox will not be sitting on anything except the mailbox. I'm concerned that the wall blocks will just crush the mailbox over time. Is there some steel plate or something that can be used to span the distance above the mailbox that would be strong enough to support the weight of the blocks above it?

The X indicates where I'm concerned about it falling in.

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