Redshoes...
It just so happens that I work for a Beatles tribute band here in Wisconsin,
The Britins , and I have produced 2 CD's of live performances. You can hear some samples on the "Songs" link on the Britins website.
The one thing I have learned about making a Beatles song sound like the Beatles, is the band using the appropriate instruments. A 60's Ludwig drum kit has a distinct sound to it. Likewise a Gretsch Country Gentleman played thru a Vox AC30. If your band uses authentic equipment, your more than halfway there.
Of course, the toughest thing is gonna be the vocals. No matter how good some singers are, they just aren't Lennon or McCartney - two of the more unique voices in music. The best you can do is try to do the songs in the original recorded key and tempo, and hope for the best.
Until the Revolver, the vocals where quite dry and unaffected. They frequently used ADT (Automatic Double Tracking) on the early to mid era songs. From Revolver on, flanges, chorus, echos and overdriving channels where common place. And not just on the vocal tracks. When we do "I Am the Walrus" live, I bring down the fader on the lead vocal, raise the gain to nearly all red, totally cut the lows and midlows, and add an effect on
the Lexicon MPX1 called "Call Waiting". It gives it the thin, overdriven, off in the distance, dry effect you hear on the record.
I hope this helped. And if you have any more questions, I could talk about Beatles stuff all day.