I'm not a fan of core's track hiem threads, they do not stay tight and hog out the bung. core does use a factory jk type bushing which is pretty flexible but use on only one end of a short arm with a flex joint, still over flexes them and can cause snap ring failure. id rather put kits in the re arms and use what you already have or spend money once and get a currie/savvy control arm set.
This is why I question the rubber bushing at one end and a flex joint at the other.