I did my mold in a very similar fashion. I had a bit more open space at the corners where the shroud met the radiator to try and get more flow at the edges (1.5" IIRC). Also non-stick aluminum foil worked pretty good when put over the mold to act as a release off the mold. It looks like you have plastic or something instead, check to make sure the resin doesn't eat it. Molding on the outside was a bit messy, but very functional.
Very nice looking mold.
Very nice looking mold.