this can't possibly have solved the overheating while sitting still problem you mentioned. Assuming the cooling system is in good condition, you really need a bigger radiator if it can't maintain temperature at idle sitting still! otherwise you are just treating the symptom rather than the problem.

but it is always a good idea to block off any unneccesary holes in the radiator support panel. I did this after having temp creep issues after a few laps at QR last summer with my coupe - the previous owner pretty much had the whole radiator support panel cut out with massive gaps either side of the radiator and a big intercooler (including its end tanks) stuck right in front of the radiator core. I bought a different intercooler and have mounted it lower to clear the radiator. Its under the bumper in a front spoiler (which are a big help with cooling on a track), and with the radiator support panel now closed off up to the radiator core I'm not expecting any more problems.