Bob,
My experience in welding a field grade LC was that the barrel material contains enough carbon to harden as the weld self-quenches when it cools. I used a low carbon steel rod "Ox-weld 65" then had to torch anneal the weld to be able to file it.

You should have no trouble welding on the barrel, even near the ribs. If you have to torch anneal a weld right next to a rib, I'd wire up the rib in the classic manner in that area.

An etching type satin finish rust blue should hide the weld well IMO.