Do you have to have the Tactical model to be able to have the o-ring barrel or can you just take a regular USP and drop it in as well? I want a 9mm fullsize with threaded barrel and match trigger but I don't want the adjustable sights because I'm planning on getting night sights for it. What is the best route for me to take? Buy the regular 9mm and get the trigger and barrel put in? or buy the tactical 9 and just get the trigger put in? Also, I need to get mine changed to Variant 2, where can I get this done at?