Dale,
Tinker is right in his advice about welding the tubes to the monoblock, this is not the place to weld. Welding on the barrels can cause scaling inside the barrels and cause the monoblock to become brittle. There would be no right way to re- heat treat the barrels/mono. after welding. Proper solder jointing will be more than strong enough. If you want an almost invisable joint you can try what Mr. Ellis Brown suggested in his second edition and leave the barrel shoulders just a little high and peen them after soldering so as to close the gap, or you can do what I do and lap the joints together before soldering. That will make the joint almost invisable. If you want the details, send me a PM. Bob H.