MStudt
official vendor
I did the same thing a while back... I switched to fronts for the rear and stacked washers for extra strength. It was nearly impossible to get a wrench or socket on the top nut to get it off to replace them because the washer had folded up around it.
Stacking washers aren't needed if you had the correct washers in the first place. One grade 8 washer on the top and another on the bottom is all you need. If those start folding up, then you have the nuts way to tight. So many people under estimate the strength of washers, and more often then none don't know how to properly match them. Over tightening your links are only going to put added pressure on the hardware rather than the bushings.