Does the barrel have a break or compensator in place now? If so it may be pinned and welded on in which case the barrel is already threaded but getting the device off will be difficult at home. Also, to change the front sight post you will need to remove the muzzle device unless you cut it the current FS base off with a dremel and then install a clamp on like those made by Yankee Hill. It may be easier and even cheaper to just get a new barrel with or without FS already in place. DSA has 16" barrels on sale right now for $110. Of course you will also need a torque wrench and barrel nut wrench so after the cost of those you may be more than a gunsmith.