Cold Case Radiator Shroud?

I've got that same radiator on my Duster 340 with the factory shroud. It is cooling well for me but I know the gap you refer to. I saw a thread here where a guy took out the mounting threads in that channel and did some slight mods to the shroud and actually slid it down in the channel for a tight fit. It looked really good and closed the gap. You can search for it here and he showed exactly how it was done. Not all that complicated and looked good.