I believe hot metal welding could be done but it has its risks. Years ago I repaired the cylinder head of an MG Midget using J-B Weld. It's a cold bonding material. I had just gotten back a cylinder head from a shop that did an excellent valve and rebuild job on it. As I was just about to apply it to the top of the cylinder block I noticed a pit in the bottom surface of the head right next to one of the cylinder bores. Upon inspection I discovered that it was directly in line with the sealing ring that many head gaskets have around the cylinder bores. An the pit hole was in diameter about the size of the dimensional width of the sealing ring. I was concerned that the pit was just large enough and positioned at just the right spot that the compression of the cylinder could blow thru the pit, undercut the sealing ring and cause a compression leak that would cause a complete failure of the gasket. I discussed it with the shop and they said " welding it up had risks" possible head distortion. I took it home and decided to fill it with JB Weld. After curing, I filed the area flat with hand files. Used a metal straight edge to verify flatness and assembled the engine. I know this engine to this day, it has been almost 20 years and it still runs perfectly.