Congrats on getting your permit for tomorrow, hope you make it and have an enjoyable experience.
Ice Ax: Snow should be manageable by tomorrow from what I have been reading. Microspikes and poles at most if needed.
Acclimatization: I have summited Whitney 6 times, Baldy 49 times (50 this coming weekend), Gorgonio 6 times, Jacinto twice, Langley twice, and White mountain once (among other peaks) and I have never had AMS go past a very slight headache that was solved by guzzling some water and eating some food. I know everybody is different in their reaction to altitude but you not experiencing AMS on those mountains sounds similar to mine. I don't know anything about Diamox but I would say that if you are good so far on your hikes to high altitude in the weeks before Whitney you should be pretty much OK if you keep yourself hydrated and fed on the way up. I would say bring it just in case but don't use it if you don't feel the need. I live in L.A. so I usually show up in Lone Pine the morning before I hike and go straight up to Horseshoe Meadows parking lot. I spend the day up there and then sleep in Lone Pine at the Dow Villa until after midnight-1 AM or so, then head up to the Portal for about an hour and hit the trail around 2-2:30 AM. BUT..that's just me, you never know what will hit you and when, so always pay attention to your body on the way up. Climbing Gorgonio and Baldy in the weeks before Whitney always helps you acclimatize. Go slower than usual between Mirror Lake and Trail Camp as this is the steepest section of the trail and you will be good to go for the 99's and the back 1.9 miles.
GPS: I have been using the same Garmin Foretrex for the last 5 years and it is wonderful. The Whitney trail is very well defined except for the rocks above Mirror Lake and right before Trail Camp, just go slow and look for footprints is what I did.
I wish you the best and enjoy that feeling of accomplishment! If you don't make it on your first try (like me, unprepared for weather) you can try again since you live so close.
