On my truck (89 standard cab/bed 22re) I have the wide u-bolts with the clam shell plates that cover the leaf packs where the u-bolts clamp down. Originally there was a rubber liner inside of them. I know lots of models didn't have those...just the u-bolts clamping directly over the leaf pack.

Anyone know what the point of these plates was?

probably cut down on noise

just a guess

Yes, that is my guess as well. Basically had a metal clam-sheel around the entire spring pack, lined with rubber to eliminate any metal-metal contact. Even the head of the center pin in the spring pack was encased in rubber where it went into the spring perch as I recall. Worked fine until you added a leaf to the spring pack or installed a thicker spring or tried to use a u-bolt flip kit, where none were designed for that wider spring perch. Have seen folks notch the sides of the perch to let the narrower u-bolts and spring plates be used.

I have a set of the clamps and rubber liners if someone is needed those parts.