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The jacking up will have 0 impact on the engine, don't worry about that.
Since the tapping noise only just started and you say the car ran well before the various mechanics got their hands on it, it may not be something serious (although it might be - just odd that it wasn't there before recently).
Looking forward to the video, I am sure that will help us all get a better idea of what might be the issue.
Just a thought, it may be pinging due to too much ignition advance, who knows.
I would not entrust this engine, if it does need a rebuild/repair, to any local mechanic; I would send it off to Metric Motors who are one of the few specialists around. They are located in Canoga Park, CA. Although theoretically any good mechanic should be able to do a rebuild, there's too much at stake to take chances and a Metric Motors rebuild will add value to the car whereas a 'no name' mechanic's will not nearly as much. But let's hope we don't need it!