If you have the 'permanent' muzzle brake attached I will second just having the barrel and front sight/gas block replaced with new after ban stuff.
Torch cutting, high speed milling or whatever technique folks are using to do these wonder conversions have negative effects on the accuracy of the barrel.
There are no real issues with having a non-braked barrel turned and threaded for a flash hider but those 'pre-braked' barrel cause more trouble than is neccessary when trying to thread them for after ban stuff.
Just buy a new barrel and be happy.
If cost is a big concern consider a new Olymipic after ban barrel, very good stuff and very reasonably priced.
A gunsmith with skill and ARs, and now-a-days everybody who calls himself a gunsmith pretty well knows the ins and outs of these rifles, the gunsmith should install, headspace, and test fire for a very reasonable fee.
I usually charge way less than $100.00.
Total cost should be well under $300.00.