[William]

Having dismantled plenty of '69s back in the day I know what I expect to see. Others may also know and commenting about it here doesn't help.

Photographing it in the car is better than nothing but could establish that it was molded in off-white plastic. With the hood open, take photos of the backside and inside top. If you can, get photos of the underside also.

If the grille is molded in black plastic we are back to square one. Doesn't prove it was built with it.

Removing the grille is some work; the bumper, headlamp bezels and grille reinforcement have to be removed first. Paint could be scratched and parts damaged. And it may not prove anything. I'd rather let sleeping dogs lie than risk any of that. I understand if you would rather not.