The Uniroyal GR70x15 was one of the 1973 Trans Am radials if you wanted white stripes. If this is an actual Uniroyal as Verne said, I am wondering what Uniroyal called it on the sidewall. Here's an example. And yes as you mention, that tread looks just like the infamous Firestone 500 tread on my 73 SD.
Uniroyal GR70x15 whitewall:
Firestone 500 GR70x15 white letter:
