Bill, Okay here goes. The faint of heart should log off now.
If you have learned to weld, you will remember that gas welding on a circle will shrink the circle because the molecules come to the heat. On the lathe, turn a rod to approximately 0.702. See if it will go through the rear bridge and into the lug area of the receiver ring. Leave it long enough to stick out past the rear tang about 5 inches. Clamp a pair of vise-grips onto the rear projection of the 0.702 rod sticking through the action. If you run scared, put heat stop paste on the rod and around the action between the front and rear rings. This should keep the receiver ring cool enough to bare hand. (Test gently) Use about a #2 welding tip and ply the heat to the top of the rear bridge. Bring it up to red and remove the heat. Try pulling the rod out. If the receiver is still loose put on a little more heat. If it starts to hold the rod DO NOT put on any more heat. You don't want to stick the rod. If you do, drive it back with a punch in the center so you don't swell the front of the rod by beating on it. That will make it VERY tight. If it is too snug, lap it with the rod and lapping compound.
Don't forget; you asked! P.S. Don't do this with the barrel in place.