About having barrels threaded for suppressors ....
The best way is to just send your gun to Gemtech. Unlike with a comparatively short "flash hider," the bullet has to travel another five-six inches before exiting the suppressor's muzzle, and the threading has to be done precisely or you can end up with bullets hitting the baffles inside the can, or the can's muzzle-end cap. Not good.
Doc Dater at Gemtech usually charges $75-85 for a simple threading, with a thread-cover cap. He also does two other approaches for Mk II's: One is to recess the crown and cut internal threads, and you use an adapter to thread the can INTO the barrel rather than around the outside of it. A second approach is he threads the barrel on the outside as normal, sets back the front sight a half-inch, and then takes a section of new Mk II barrel and makes a thread cap out of that. When screwed on, the barrel/cap seam vanishes and you can't tell the gun has been modified.
HTH.