When you pull your bumper off to work on it, check to make sure you have all four of the locating studs (2 at the end of each bumper). Those tended to break off over time and they are needed if you want to have your bumper fit flush with the rear quarter.
Some info. here;
https://forums.maxperformanceinc.com...d.php?t=793726
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Peter
1974 Trans Am, 400 4-speed, 3.42 rear.