Years & yrs ago there use to be a process call furnace bronzing---where they could repair cracks in heads/blocks. They clean, boil & strip the head/block then dip it in a special hot acid ( sequence of procedures ) then fire it in a furnace red hot then braze/bronze the cracks. I don't know if this process is used anymore or if ended up not feasible do to the elaborate castings of today or price of replaced parts cheaper then the bronzing.