Basically it all comes down to the fact that the older style front panel hasn't been available for many, many years. The same goes for centre bar grille parts. Means that if the pre '65 cars got damaged or had rust problems, a new style front panel and grilles were easily fitted. To some it was considered a modernising upgrade. It's even harder now to change back to the original style as the grilles are very hard to find in good condition.