I have an XO-2 and $400 for an XO-3 sounds high. I know the XO-1 models really command a premium. The OX-3 has 26" wheels and the AD is most likely 27" or 700c. If I had this choice, and the AD is not dented or really damaged, I would go that route. If you want mustache bars, Nashbar has there steel ones cheap.
Just read cuda2k's comment and I agree with his suggestions. For that matter an early 80's mountain bike with slicks and handle bar swap would work really well too.