Just an opinion:
As cheap and easy as it is to get a chunk of 9 mm bbl blank,you have lathes available...and you are pondering cutting threads over threads,or welding and?????
The shortest distance between two points is a straight line.You have a ruined barrel,scrap it,put a new barrel in and do it right,the first time.
IMO,if you are dealing with gunsmithing ,barreling and chambering,there is a standard to work to.You do it right!You do not know who may put their face behind your work.You take part of the face or sight from someone trying that piece and you own it.You did it.
If you want to play around and do something creative,make sights,glue wood on,add a recoil pad.That won't hurt anyone.