Roys101, Welcome to the forum. We have an area called "Introductions". Stop by and say "Hi".
Now, why would you consider ruining such a fine pistol in its old age?
Barrels already threaded for a suppressor? I don't think you will find one.
And I would suggest that you get the okay from BATF for the suppressor before even a trial fit. They monitor this site, and can get the info needed to track you down.
Boring the barrel is not a good idea. There is a crown on the barrel and removing the crown will have a detrimental affect on accuracy. It is not a good idea to install a suppressor and then have the bullets yaw and destroy the inside of the suppressor. Plus the remaining material will not be strong enough to support a suppressor if you bore out and tap.
My suggestions? Sell the gun, buy one with a threaded barrel, get the okay from the BATF for a suppressor, and have fun once you are legal.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC
Former President of the ECPT (Eifel Combat Pistol Team)