Hrm, with 300w it looks like trouble at 34hz and below with respect to air speed. And 24x24x24 is 8cu (not considering wall thickness).
If you can fit a 22" long port in a 2cu box then I agree it would offer bang for the buck. I think I would still prefer the HF personally. Would give more HT options if you decide to build a new box. But then again you actually have both drivers so I guess you are the expert

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