If you have a new USC barrel, I would have that cut and threaded, since you know it's history. Or, keep it as a title 1 til you SBR, and pick up a spare USC barrel so that you can cut one and have one if you ever need to remove the SBR from the registry and need to revert back to a rifle. Stuff happens, maybe you need to move to a state that does not allow SBRs, etc.
And yes, Tom Bostic is 'the man'.
Also, welcome to hkpro. A den of 'enablers'.