I gotta say your shroud looks ****. You could probably sell it once you build one that works. I'm gonna go take some measurements and design a shroud. I have a Koyo rad and those slim fans sitting in my room. Though my Koyo is the big one, which is more than 37mm IIRC.

 

The shroud sits on the end tank seams which are about 5/8" from the face of the rad rows, so there's a 5/8" gap from the row/surface to the shroud surface.