Thread: threading odd muzzle

You would have to ream it out inside
Re crown down in there
Put an internal thread in there
Make an adapter bush with a hole with enough clearance for the projectile to pass through

I would locktite to bush to the suppressor so the muzzle will look completely normal with the suppressor removed

Not that hard too do
Just tricky and one off
Your local gun plumber would hate it
Just turning hours into dollars for them