The 67-70 brackets Are shorter due to the fact that the outer mounting holes are about dead center of where the 71-72 parking lights are in the bumper. When GM put the parking lights in the bumper in 71, they had to make the outer holes farther out toward the edge to miss the parking lights.
I have a set of 67-70 brackets if you are interested.
http://67-72chevytrucks.com/vboard/s...d.php?t=573006
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