Attacking the problem the wrong way.

Here is a standard 14-1lh to 1/2x28 adapter, and what is does it to use not only the barrel shoulder, but the OD of the barrel to lock the adapter in place to stay parallel with the bore.


So since the SilencerCo Trifecta flash hider is going to be permanently silver solder to the barrel, then it just needs to be counter bored to do the same thing with a over lap on the barrels OD as suport, then it silver solder to the threaded barrel to end up with a 16" title 1 barrel and it permanently attached to the barrel parallel to the bore so you don't get a baffle strike.

Flared shoulder will work as well.  
Hence barrel is over thread so a threaded section insert can be threaded on first, then is profiled  and end faced  squared to the bore, so when the FS is attached, it too will be square to the bore as well.

Bottom line, either way will work fine, and since you have someone that can achieve that you want in the end, let them do the project.