Sadly the GT40 ran a different style Halibrand (now dubbed the champaign glass style), that ran extra webbing up to the extended centre boss. (the one you have modelled is a VERY accurate Halibrand but not one that was in GT40 use in the 60's)
Something I saw at a recent car show, the rim lip done body color and the center polished.
Craig, thanks for the heads up. Saw a pic recently and did notice some differences but wasn't sure if there were different versions of Halibrands or if it was an innacurate copy.