Holy smokes, that is some fantastic documentation! Very special car. Dont let a few minor setbacks make you want to sell the car. We have all be frustrated just like you. Removing the headers for the second or 3rd time is super irritating but you may think about possibly pulling the engine to regasket it since you are already needing to hang new freeze plugs , especially in the back ? Make sure to coat the bore holes in PTFE sealer before you put the plugs in. I had to learn this the hard way in my powerwagon 360 but now could probably pull one of those engines in my sleep due to multiple times fixing newly installed freeze plugs.
