If the clutch unscrewed CCW, then it would unscrew itself as soon as the chain hits the wood. Those old clutches with the fibre shoes and the soft aluminum spiders and the thin sheet metal sides are easily destroyed by the hammer-and-punch method of clutch removal. For those clutches I keep a matched pair of 7/32 shanks that I insert under opposing shoes after carefully prying the shoes outward to avoid chipping the shoes when inserting the shanks. As stated above the vise jaws grip the shanks while the saw is turned while the piston is stopped. Remember to pull out some slack in the starter rope before you stop the piston so that when you retighten the clutch you are not pulling against the starter mechanism.