Can't help you from experience, I assume you'd make fitted vise shooes to hold the frame and a make a good fitting barrel wrench, when you put the new barrel in you'd have to creep up on the fit so that the barrel torques tight just as the front sight comes in to line, which would mean you'd need a lathe to peel the shoulder a few thousandths etc and try again.
But I wanted to ask what happened to the old barrel?
I have CNC produced 416 stainless triggers to replace the plastic triggers on Colt Mustangs, Mustang Plus II's, MK IV Government .380's and Sig P-238's. Video on installation in Sig;http://www.youtube.com/watch?v=Jh2v_-87DRM
Plus Llama .32 and .380 recoil spring buttons, checkered nicely and blued.