Dear Iain, Jerry, 65GSConv, and mid-60s Buick caregivers,
Thank you all for your input. I assumed it was 1" but then saw many different ww width on coker tire website. So, I sent them an email asking what they think was stock for this year and combo.
I haven't considered any other companies yet,
. . . .
FYI: Biquette had a set of Coker tires put on in 2010. As you found out they are more like 3/4" instead of 1". It is a subtle, but noticeable difference. Here is a photo of Biquette back in 2010:
In 2018, Biquette was fitted with larger tires with true 1" white-walls from
Diamond back tires:
https://dbtires.com/Here is a photo of Biquette with her new tires:
I wouldn't be surprised if even most purists wouldn't notice the difference, but I really like the additional width. The additional width is enhances the contrast with the rest of the tire and really gives that 1960s look. Alas, Diamond back tires tend to be more expensive, but you keep an eye, they do have sales from time to time.
Cheers, Edouard