The length of the shroud is critical to correct fan performance. The fan blades should fit halfway into the back end of the shroud, so the fan hub is just even with the rear of the shroud. Too far forward or back will result in incorrect air flow through the radiator, and/or oddball noises. Also, any areas around the sides of the radiator should be covered with sheet matal, so all the air passes through the core. That's not usually a problem with a stock radiator, but on a custom job, sometimes it gets forgotten.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!