1968 340 timing

What you posted above is not a problem at all. Many ignitions generate a spark on power up. So if a piston is in just the right position, and a cylinder is charged, it COULD actually start. Also, many newer tachs 'stick' at whatever RPM they were showing at the instant power is cut. Autometer does this

So far as the advance banging on the firewall, I suggest you re-read this thread. All you need to do is rotate the dist body to a more comfortable position, set up the timing marks, and rotate the plug wires appropriately.

It may be the dist. drive gear is not quite correct, or that you have one of the "oddball" distributors with the drive tang "different." There's no need to fight with it.