Well, DJK [who I trust] says it's 620 size, which is 9 ft^3 gross and Bill recommends 9 ft^3 net, so figure out what its gross will ~ be with the driver, bracing, and divvy it up to whatever H x W x D you like, though preferably make the W x D some golden or acoustic ratio to minimize the amount of internal damping required. The driver, vent location should be at odd modes in a high aspect ratio cab same as the speaker, listening position in a room, i.e. at ~ 3rds, 5ths, 7ths, etc., of its inside [i.d.] height .

FWIW, putting the vent close to the driver is all well and good in a typical rectangular cab, but the 'V' has a high enough aspect ratio for some minor ? WL TL pipe action to help damp the vent [and ideally should be taller], so placing the vent much closer to the bottom is a good plan for a theoretically smoothest response whereas up high it adds a second reflection that creates a broadband notch in the upper bass, defeating any TL pipe action.

Basically, the 'V' should sound like a big reflex unless the cab is relatively densely treated to roll off any peaking at tuning [Fb], but normally the goal is to maximize acoustic efficiency, so not a good plan.

Bill?s a successful horn designer, so has to know this. I guess he just chooses to stick to tradition for tradition?s sake and/or his main market wants it that way.

Regardless, you want more bass, then you need to go larger, tuned lower, so how big in H x W x D can you ?afford? and how much, if any EQ [and type] are you willing to use?

GM