Threaded barrel, different recoil spring (if you want it to function), silencer of course, sub sonic ammo with enough power to move the slide, barrel and silencer mass in the "short" recoil stage. Insufficient power ammo will cause short cycling and too much power with light bullets will cause a sonic "boom" as the round breaks the sound barrier. Ideally, if you want a really silenced 45 you need to either get a pistol designed as a locked breech non self loading or put up with the noise of the pistol cycling and the silencer huffing and puffing.