The throttle return bracket design changed each year. For 1968 it was a short L bracket that mounted under the carb stud. In 1969 it was a long bracket that fit under the two rear carb studs. In 1970 it was a bracket that mounted to the intake manifold itself. The return springs changed as well. In 1968 a black return spring was used, and in 1969 a gray return spring was used until April 1969. Then after that a yellow return spring was used. The different colors indicated different lengths and coil tensions.