I don't think that's an old commercial at all, for a number of reasons. The WSM has the new style door handle and the barbecue has the new style wheels, the aspect ratio it was shot in is wrong, and the soundtrack doesn't have film hiss and the speed stability is perfect, and there's no film grain.
Heck, the fact that there's a WSM at all means 1981 or later and I think that was done recently.