Dave,
You generally don't Tig weld the barrels and monblock together, they are soldered and/or threaded. The welding he is talking about is to have his forend hanger bracket lightly welded to the barrels. Some builder also weld in the mid spacer or the front sling spacer as some call it. I don't like to do that because it limits the amount of adjustment after you weld it in. If you have problems after doing that, the spacer will have to be sliced back off. I just solder mine spacers in. The only other welding that needs to be done is sometimes it is necessary to weld filler shims to the forend bracket before welding it to the barrels. Bob