Tigernut, as was previously mentioned by other members, the speaker grill has a reputation for an incorrect or should we say , sloppy fit.
However with the time and energy spent restoring the car, the restoration, or fitting of a speaker grill is not a big problem
With a little time and some special care, it may be carefully bent

in order for it to conform to the shape of the opening in the top of the dash. I have just finished fitting one, and once in place, you can't fit a dollar bill between it, and the fiberglass dash, anywhere around the perimeter
Drive your Corvettes

as if each day was your last