i noticed when i took the shackles off one time that the bushing had worn a dimple in the shackle plate, Toyota has two different ways to combat this, a shoulder on the "bolt" which is pressed into one side of the shackle plate, or a bushing housed in a metal sleeve, with another metal sleeve in the ID of the bushing, all vulcanized together, and pressed into the eye of the leaf spring...
both of these methods eliminate over torquing the bushings... i think something along these lines is what i might resort to in the future