V both pieces on
all sides, weld them of & go over size in all areas, let them cool, grind or belt sand them close to finish size & Do NOT get them too hot in the process, file them to finish size.
I have done Dozens of them for me & others & use just regular wire in a wire welder & mild steel for the tang. Only ever had issues with one & turned out the new wire they welding shop gave me had changed & they didn't know it, was a manuf. change. Went back to the old Harris wire & no problems since & welded ? 8-10 since with no problems.
Have welded lots of cast triggerguards with same wire. ALL of the tangs & guards browned with no issues..