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With good wires it won't matter but, it is good practice to keep them apart wherever possible. This prevents shorting or cross-talk between the two. That is why the stock brackets and guides place the wires so neatly apart.
When two conductors run close and parallel to each other a sudden surge of current in one can induce a current in the other; this is the source of "cross-talk" between wires.
With spark plug wires this is only an issue with the #5  SBC wires due to similar phasing of the compression strokes.
As mentioned, performance wires are spiral-wound to virtually eliminate corss-talk. If running stock wires put #5 in the top separator slot and #7 in the bottom slot.