[Floyd R Turbo]

Interesting fixture you found there. I've been trying like crazy to find endcaps like the ones that come with that fixture to no avail - they're always sold out or something, possibly discontinued.

As for the build, I agree with srusso, clean the 4 lamp side and rotate the 2 lamp to the 4 lamp side. Of course, just use your judgement. I think (emphasis on think) you will get good growth if you are using the fixtures I think you're talking about from eBay (top dog or something is the seller).

One thing to note, when you say "doubled up screen" are you thinking of using 2 screens back to back? If so, do not do this. If you rough up one screen enough, it will have all the algae holding power you need. Double screens were attempted and the result was to advise against their use due to many factors.