Great job Paul!
Let us know if the coolant overflow persists. Hopefully it's just "burping" itself.
Since those headbolts are a one shot deal, you might want to replace the front two. You could grind a very small amount off of the end (like 0.5mm) to ensure that they won't bottom. It's possible that you got some gasket material in there and it's probably really jammed in the bottom of the blind threads now.
What did you decide to do with the dropped washer? is it still in the bottom of the pan?
Also, please comment on the before/after power characteristics.
Thanks for posting the great pics.
Experience is something you don't get until just after you need it.