I use Rob Grunter's method of rebuilding anvils which has the pre-heat and post-heat temps. If the face is loose I would remove all of the face which is loose and leave what is not. I heat up an anvil with a weed burner and check heat temp with a 400 degree Tempil stick crayon. I rebuild starting with 70s2 welding electrode which is a mig wire. I use Stoody 965g and had luck so far with it. When starting the first pass on the edge I clamp a piece of copper block against the side and lay a piece of 3/4in steel under the other side of the anvil to tip it to the copper for a thicker weld bead. Hard-facing does not like a long arc so it needs to maintain a short arc for porosity free welds. The 965g Stoody which I use is a 2layer recommended and a 3 layer max, do not exceed the max. Make sure the anvil it heated and cooled properly each time you weld on it. When finished welding, I grind it down with 7in Dewalt and 9in Milwaukee angle grinders, one with a Norton, Norzon Plus flat stone, and the other with a 6in cup stone for flatness. This is just my way of doing a re-build, but I am sure there are other ways of doing it, just don't sway to far from Rob's process. If I remember correctly there was a blueprint on IFI which used a 7018 rod for in-tel build-up and finished with a hard-facing rod on top. Sounds like a lot of work but it is kind of fun.