I've done something similiar, weir rather than toothed, and with overflow boxes on the outside as shown:
It only projects 1" into the tank plus glass thickness (3/8") plus slate thickness (.25"). It's nice to not have to limit the flow in the tank-holes by needing a bulkhead there. 'Course, coulda just made a bigger hole if needed. . .
I did end up putting braces within the internal overflows (to left of hole in tank in the second pic), but they are nested about 1/2" below the lip to rest eggcrate upon.
I intend to put stockmans on the 4 x 1" bulkheads on the external boxes. I wouldv'e probably made the external boxes taller, but this glass I aready had lying aroud, and just had it cut professionally. I would have prefered to have a single long weir with two holes draining to a single larger external box. But watcha gona do? Yes, that is a triplet stroller at the top of the third pic. Some projects take precedence over others (says the wife)
Any thoughts on problems with the shallower boxes?
It isn't up and running yet, and won't be till after our move at the end of the year. I have high hopes. Per DonBossung's advice I'll consider running the drains from the external overflows separately to the sump (I have 1.5" flex-pvc). THoughts re noise/flow?
This is a brackish tank, not reef, so the slate shingles are my background, without hope of ever being coraline-covered.