Goodyear, Firestone and BFG were the big dog companies for muscle car tires. A 71 Buick GS sure is sweet. My favorite GMs were the 67-69 GTOs and 68 Olds 442. I almost had my father buying me a 68 Shelby 350 luxed out with options but unfortunately he wanted to drive it first. I ended up with a fastback 67 Barracuda.
Im still thinking about this.... Another source of info would be to contact a car collector person or a company specializing in muscle car restoration. Hey! Call Danny Counts in Las Vegas! Say hi to him for me too! Lol...
Okay.... Just did a bit of searching for you on www.duckduckgo.com using classic tire keywords. 2 minutes searching and 5 minutes on the website below looks promising for talking with some specialists. Heads up that you could end up with the P-metric equivalent to the G70. Also, consider a redline tire as an alternative to the white letter.
~~~> https://www.performanceplustire.com
I’ve given up on the ‘white lettering’ option- you never know what the dame fools will do next, so I won’t prominently display any corporate advertising anymore (with notable exceptions for known good guys)