using a torch is fine for heavy metals, however use correct tools for the job at aren't always cheap. using a torch until cherry is good for heavy metal but your frame rail is considered sheet metal, an inexperienced user or novice may overheat the sheet metal and stress the sheet metal causing cracks in sheet metal. the safest and best way with little chance of bad side effects is to use an Induction Heater, place the Induction Heater on the item to be heated (in this case k frame bolt)and it will only heat the item it is touching,heat until red then let cool off to the touch spray a little PB blaster , a breaker bar and try screw it in first to breah the bond then try to loosen. you may have to repeat the process , but most generally not.remember as someone else mentioned earlier the back and forth motion is best way.