4 screws and a collar nut. The trigger bar/spring will pop out as you separate the two halves, and is a balancing act to get to stay in place when you put the two halves together again. The hammer, sear, springs, etc are held in place by the safety lever and won't go anywhere.
What about swapping barrels?
As in, how does the barrel attach to the pivot block? Is it threaded with a locknut? Or pressed/permanently attached?
Be cool to get a .357 barrel for the Sub-9 Trifecta! 😎