Nice work... With your thread title, I thought I'd see some crap ghetto stuff... but, I was mistaken. Very cool stuff going on here (I have a pirate fowlr tank for the wife), more more more!
... I too have a 240, and used all return pumps for flow. Yet, I drilled about 4 holes along the back wall and each has a split locline attached on the interior, one is a spray bar behind the rockscape. All are powered by (3) mag pumps. A Mag18, Mag12, and Mag18 in that order. One pump is split via a SCWD, and provides a bit of alternating current. I can't stand powerheads. They're unsightly, and a pita to clean around. I hope you can get the proper flow your looking for!!
All in due time! I'm watching the progress!
And your too small of a sump issue... why can't you upgrade the size of it (did I miss that)? I'm using an 80gal glass tank for a sump, and it's nearly too small for what I've got going. But, it works and allows for just a tad bit of siphon. BUT... you've got 40gallons of siphon?! Holy cow!! Why so much? Can that be changed with piping moved up closer to the surface, or something to get the height corrected?