Block drain wasn't needed when I did mine.. just simple radiator drain and that takes levels down below the valley plate. There will still be residual coolant in the valley but nothing will pour out elsewhere.
Still solid a few thousand more...
Still looks like you're good just from the coolant level. For the boroscope, most of what I've seen has been on the driver's side of the head. Plenty of folks have shown no external signs of a leak and then when they open it up, it was...