I adapted several barrels years ago for ARs, but sold my extension wrench and reamers when I stopped building ARs. I found a barrel I have sans extension. I can turn barrel neck to fit the extension, but without a wrench its not gonna torque up. I dont want to muck up a bolt just to tighten it. I also dont have reamers anymore (can rent them) to finish for a bolt. To buy and rent it all, heck I could buy another barrel. BUT hey it is a project. Maybe some gunsmith has the stuff and would do it for a reasonable price.
Man go to Blackjack Gunsmith, ask for AJ, He is a great gunsmith, He build my remington 700, installed the new heavy barrel in 308, did the thread for muzzle breack, and the glass bedding on the new HS stock.