I read over your build thread to get a sense of what you are working with. You say you don't have room for external boxes (via a ghost style overflow, eg) but are considering drilling the sides? I must be missing something obvious but if you have room for a bulkhead and elbow, why not a box? I think you should be able to have a slim ghost style overflow internally (running the full width of that side) and use an external box that fits between the joists. I'm not sure what that width is, but if it is enough for 3 holes you have your bean. You would not need 2" bulkheads, I think bean's original setup was pushing 2500gph and he used 1" bulkheads with 1.5" pipe.
I don't know if you still use the 3 way valve, bean will need all 3 lines to be independent to the sump. You could bring you return up and over the opposite side and create a nice surface flow to help push everything towards the overflow.
Btw, reading that thread from the beginning has left my mind blown. Do you still have the tiered water feature in the back?
As always will tag along to see what you come up with.
- Ian
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