This pair of catalog numbers has very high similarity between the normal and the Farley special printing. Both are perforated as Peter notes. Main difference for 752 is the lack of gum (which could be removed from 727) and the position pieces showing gutters due to the sales in sheets of 400. Used singles would be identical, except in very special cases. You will want gutter pieces for 752.
One way to possibly tell them apart when used is that a careful examination of the back of 727 will frequently show traces of the gumbreakers left in the paper when the stamp is held at an angle. Hold it in the flat of the hand near a lamp just under the level of the eyes. However it does not show every time; when they are seen it is clear which stamp it is.