This worked! Can't thank you enough. I appreciate the solution so much.
And I now see what I had been doing wrong in my initial CSS solution attempt, too. I needed the side-by-side wrapper tag and not the masonry tag.
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This does now all make me wonder, though, if using the Blog feature was even the best feature to use for this story. Would I have avoided all this hassle if I'd chosen a different type of SquareSpace section? Just wondering if there's a different feature that would still be able to present a side-by-side summary layout, and have pagination links at the bottom of each page, which wouldn't be subject to the blog post ordering.