Are they including bulkheads? If not, you need to make sure that 1 3/8" is appropriate for the bulkheads you get. I'm guessing that would be for 1" PVC
, so you can figure in about 600gph for each... assuming you've got a relatively straight path down to the sump. Might be best to assume 500gph each and match the pump w/ head height pretty close to that.
What kind of overflow box are you using? Your description almost makes it sound like they're just going to drill 2 holes anywhere in the back. You need to make sure that they drill them in the appropriate area for your overflow boxes so that your water line isn't way too low or too high.
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