Yeah I tried putting the fans in a pull configuration (above the radiator). From my recollection, the problems included at least 1) mounting (given the case's incorrect hole spacing and screw clearance problems), 2) even less room for GPU power wiring below, and 3) an even more severe clearance problem with the radiator's pipes (given less distance to CPU / shorter curve radius).Normally I would vouch for Sergii work as it has been pretty good to me. But that case does not look great. I completely understand the frustration, and agree with you with a bit of it. For the refund part yes. As you have several defects with the case that should warrant a partial refund if not majority refund. But like you said it was a custom case. As for little bits of help. You could orient the fans differently on the AIO and make them intakes instead of exhausts. That will allow both fans to work. And custom cables would help quite a bit.
Custom cables would definitely help with the PSU (I wish Corsair did a better job with its stock wiring on the SF600...), so will probably go that route for whatever I move these parts into next.