I would suggest looking for factory press photos of 1979 Firebirds. Most will be of the T/A which has white letter tires. I get that. But out there, there has to be some decent 1979 Redbird factory photos or have a look at the 1979 Pontiac brochure to see what other Pontiacs had whitewalls, and go off of that.
Have a look at the following based on a quick search:
I like white walls - most people forget that Camaros and Firebirds had them. If you search the tire number for the P-metric equivalent you will find lots of info
Tim, you're fortunate to at least have a choice of stripe width for a WW tire. I know that they are not that common any more compared to what used to be sold - certainly in North America anyway. You may not easily find the definitive answer on your question... I suggest you go with what you think looks best. Personally I think the wider stripe looks better (see the last pic posted above). Cheers
I've got a Ralley II wheel in the garage with an original radial tire on it, from the late 70's. It's never been mounted, so in perfect condition. I'll try to get the tire size and white wall dimension for you tomorrow evening.
I think that Bob is right, I will just have to go with what I think looks the best.
As his images show, some F bodies had thin stripes and some wide. Suppliers of US tires / whitewall tires are few and far between in the UK but i will track one down and go and look at the tires in person.