fan spacer question

how does one determine the correct distance that the fan should be from the radiator??? i know there are different spacers.....different fans.....and different radiators. i am using a spectra (auto zone) new radiator in a 67 cuda witha 440 and i was planning to use a bolt on fan , meaning non-clutch type.....but im not sure if the clutch type is better or not???

my 440 is not an overly Hi-po motor its all stock 67 out of a 67 GTX now planted in a 67 cuda ....thanks for any input .