Hold the shock in your hand about mid point. with the flat part of the eye against your anvil or large flat area of your vice to line it up keeping arms length. Raise arm with shock up over your head and swing down hard smacking the eye only against the anvil. Sometimes it only take one smack but I usually rotate around they eye and do this.
I learned that trick in a fit of rage with a shock that would not budge after heat, oil. And every other trick. I just got mad and started beating the shit out of the eyelet against my vice. I stuck it back in the vice ready to just reef on the body one last time and it litterally unscrewed without the strap wrench.
Rubber strap wrench works good if you keep the metal clasp from making contact with the body if it still takes some force.