From the archives here:
As per DSA, the StG58A barrel is left-hand threaded, as are some of the Flash suppressors they sell.
Since the FS is silver soldered to the barrel, you will need a fairly hot flame, MAPP gas at a minimum, Oxy-Propane or -Acetelene would be better. Crucial to the process is an anti scale compound applied to the bore to protect it from damage. Brownell's should have this, and perhaps a welding supply house. Insofar as possible, apply the heat to the muzzle device, not the barrel itself. When you are close to the right temp, have an assistant apply constant pressure to the FS in order to remove it quickly and avoid unnecessary heat transfer to the barrel. Have a bucket of water handy, and wear thick gloves. Count on refinishing at least the forward part of the barrel, and don't forget to remove the handguards and/or any springs near the front of the rifle.