Did a double take on this. For just a second, I thought it was a customized 63 Grand Prix.
Then I saw what looked like a Cadillac emblem on the C pillar (or sail panel).

It may be a custom made emblem for the prototype. This emblem, which looks similiar, was used on the 1969 model:

https://i.postimg.cc/pLbW2hCC/0.jpg

I'll go back to the original photo and blow it up and post it.

Here's the emblem:

https://i.postimg.cc/g0BkbMTX/9a.jpg

I've never seen tires like these before:

https://i.postimg.cc/cHpxrvZd/9.jpg

This car also has redline tires and brushed trim rings from 1969, not available for 1970.

Unique Factory Tires
 

These original tires still remain on my friend's '68 Toronado survivor.

I picked up a pair of those unusual Uniroyals in a trade deal.Found a vintage ad in a magazine for them later on..Pretty unique.

https://i.postimg.cc/Dwbs8X1M/s-l400.jpg

https://i.postimg.cc/nLbm7hkc/s-l400-1.jpg

Sorry for the small photos - all I could find