Hey thanks for the measurements

 

Having spoken to an engineer today I feel a lot happier about this issue. Radiators grilles are tough. Basic road detritus such as small stones might bend or (very occasionally) break a fin or two but the radiator will still happily function with a 10% fin loss. Something like a nut or bolt might crack the radiator enough to make it leak but then it would probably take out a headlight and/or the windscreen too so it is really an extreme case. Take a look at the Mitsubishi Evo VII or VIII and notice the very open radiator on that car. Now remember that the Evo is essentially a rally (autocross) car and designed to cope with dirt tracks and rocky roads. No problem.