A rubber pad (can be made of the sidewall of an old tire) between the spring and perch will reduce sound emanating from the differential...but as I hopefully said earlier, it is mandatory the locator pin mate with the hole. These were used on lots of GM vehicles. Somewhat less important in an old pickup, however in a unibody car (like the Camaro) if you don't have these you probably won't like it:
https://www.camarocentral.com/1967_1969_Multi_Leaf_Rear_Spring_Rubber_Mount_Pad_p/sus-150.htmIf you're removing and reversing the center bolt, please note: many spring makers stamp the top of the bolt (above the nut) to keep it from ever coming loose. If that is the case with yours, you'll need to buy new locating bolts / nuts as the threads will be damaged when you remove them.
