Barbara Bach for Alice?
I think George could be a great cynical White Rabbit, and Ringo a good King of Hearts.
That's perfect right there as far as the Beatles themselves.
On Alice, what about Mia Farrow?
All these actresses are pretty old, actually. Lennon being the massive Carrol fan, even throughout childhood and adolescence, would have insisted the story be wholly intact, including having a proper little toeheaded child actress play the part of Alice.