Dylan---I don't think they'll get anywhere near 40, the book says an 80hz cutoff. Those are awfully short horns and don't seem to have the bass reflex augmentation of VOT boxes.
On the other hand the corner placement may help. I dunno. I reckon if you build them you'll find out.
Might be worthwhile doing a fiberboard mockup of half of one, one 15, sitting it in a corner and see how low it goes. It should be pretty easy to just make a quick and dirty flare and rear chamber.