my 2/100c worth , If you are fitting a kenlowe as a standby , for the viscous fan failing , then maybe not a bad idea , belt and braces !
If you fitting it to try and boost your cooling with a perfectly good viscous fan fitted then its a waste of time , as the viscous will move far more air, and at higher speeds the ram air will do the job anyway .
A defender should not overheat if is maintained in good operating condition . I had a 130 DC HCPU in Australia that would quite happily operate in 40C+ pulling a GTW of over 7,450kg up[ long inclines . and was factory standard apart from a snorkle . HTSH