Yes, by 1970 most (but not all) of the cars running in the Trans-Am series were running a 4-wheel disc brake set-up. In 1970, the Trans-Am series started allowing aftermarket brake calipers and rotors. I know that Girling and Hurst-Airheart were some of the brake calipers that got used at that time. With that being said, the factory JL-8 type of brake components were still being used by some competitors and were popular to other teams besides the factory guys because of the more affordable nature of those items.