I would have changed EVERYTHING. First off, I would have made Anakin and Obi-Wan be about the same age, since Sebastian Shaw and Alec Guinness were around the same age, as well. I would have put the Clone Wars as ending much earlier - old EU sources established the Clone Wars ending 35 years before ANH - plenty of time for the Jedi to fall into myth.
The Clone Wars themselves I would change. When I was younger, I always assumed that the Clone Wars were fought over the sensitive issue of cloning, while the Thrawn Trilogy by Timothy Zahn suggested that the clones were an outside menace that the Republic and the Jedi fought against. Also, the Mandalorians were established as the "bad guys" in the Clone Wars as well, in early EU material (and in the ESB novelization). The Republic doesn't need a clone army...just recruit like ten guys from each of the 1 million planets in the Republic and whammo, you've instantly got 10 million soldiers. It would be easy to make an even bigger army the same way, almost instantly.
And I would most CERTAINLY get rid of the "Boba Fett is a clone" thing. Of all the stupid shit from the prequels, that was the most offensive thing to me, especially since Fett's backstory in "The Last One Standing" was so f*cking cool.
As for the storyline itself...when you watch ANH, when Obi-Wan talks about the past you get the feeling he found a young MAN named Anakin during his adventures in the Clone Wars. Who knows what brought Kenobi to Tatooine, but that's where he would have met Anakin. Maybe Anakin really DID do work as a navigator on a spice freighter originally, but he obviously lived on Tatooine and was a great pilot.
Maybe Obi-Wan met Anakin at the Mos Eisley cantina - how else would Kenobi know that the cantina is a great place to find talented pilots?
Befriending Anakin, he fills his head with tales of glory, and war, and the wonder of the Force, all of which eclipsed the monotony of his safe, boring little life. Against the wishes of his brother, Owen, Anakin leaves the family farm and all of its mundane responsibilities to fight in the Clone Wars, "on some damn fool idealistic crusade" and hopefully return as a Jedi.
But he never does return. Instead, Obi-Wan comes back with a baby, a tragic story and an empty apology. The baby being all that's left of his brother, Owen raises him, hoping never to send him along to share his father's fate.
When Obi-Wan returns, lightsaber in hand, to "Begin the young lad's training" Owen realizes the old wizard thinks himself a warrior and exile, and views the child as a weapon he's forging for a future continued battle.
Dead set against continuing this cycle of exploitation, Owen banishes Ben from his home. But the old man waits, knowing the call to action will come.