If they go where the front of the spring attach to the rear frame rails, are they a rust repair item? Why the hole in the middle, then?
On initially looking at them, with that big hole in the middle, to me, that would be where the end of the center register bolt would be, with the outer holes being where the u-bolts go through.
Rear shackles are not quite so generic as might be suspected. Sure, there would be a certain metal spec as to bending and twisting, but getting them "made" is where the main costs would lie. THEN, those generic-looking rubber bushings and bolts are not so generic, having to be stiff enough to control and soften suspension movements against the body. For example, the stiffness of the rubber is important in these functions. as are the bolts, too. Ever watch a street/drag Mopar with the rear of the leaf springs unclamped, at the starting line and upon take-off? It can be quite educational as to how much torque those shackle assemblies take. That's with the car moving in a straight line, much less braking torque and cornering side loads. THEN consider getting those straight pieces of metal bent to fit the chassis configurations on some cars.
NOT quite as generic or easy to build as might be suspected,
CBODY67