Just advance the timing and kill the engine. If it doesn't kick back against the starter, repeat the process until it does, then back off the timing until it doesn't kick back. Then drive it and see if the overheating is gone. If that works, check the timing and note the advance for the next time you tune it. I've never heard of an engine overheating due to too much advance. With too much advance you either get predetonation or kicking back against the starter, making starting difficult. Modern fuels also need more advance that the book calls for.
