Well. I didn't expect such a great response. I've learnt a lot from all the replies and will crank that in.
I did see the Lights many years ago on a JL flight from Tokyo to London; they appeared after leaving Anchorage ( remember ANC? I still have a duty-free bag from there.)
Capt. Mahout (aka Jumbodriver) gave a great website which I will repeat here
www.gi.alaska.edu/AuroraForecast
As to my question as to whether 29A actually has a window, I'll wait until my outbound flight and then use MMB to change as needed.
Again, thanks to all, and I'll report back after my flight.