What are the chances of  sucessfully hand threading with a die for a FH (after the AWB)  Any chance a Colt 6400C barrel is the right dia. under the pin on to do this?

Your postban barrel is likely around 0.700 right now.  The barrel diameter has to be turned down with a lathe to around 0.498.  Threading with a die is easy, as long as you start with the correct diameter.  That's where the hard part is - getting the barrel turned to the right diameter.

Still waiting for the first WECSOGer to come out with their "I reduced my barrel diameter with a Dremel and threaded my own barrel" story.