Trunk hardware
E78-14
It's 7 from the bolt mount to the level when the level is sitting flat. Add 1/4" for the bolt mount to the well floor.
So, any tire over 5.75" section will sit proud in this well. Dana figures 6". In either case the factory tires could not have sat flush. Either there well was made deeper by '70 or they used a small tire for the filming so it had more visual appeal.