...being one of the resident internet expert's I thought I better get in on this thread as well.
Don't have a clue, you've covered the bases nicely.
I did like Rick's idea of under water testing for bubbles, I've had good luck with that finding very small leaks in tires. I don't currently have any freon or gas type leak detection tools, so a water bath would have to do for me.
Taste of glycol is a key element in this exercise, very telling.
On removing the heads: Head bolts no problem, HEADER bolts are a PITA however!