Putting a 29er wheel in front will add (622-559)/2 = 15.75mm of extra height, assuming you keep the same fork travel. That's probably as much as you can safely add, beyond 2-3cm bets are off. That's not to say some people don't go further, and aren't boasting how "slack" their headtube angles are, but again, for XC riding you want quick handling. Be aware that going 650b would also rise the BB, which again influences handling. Nowadays' bigger tyres add another cm or so. Again, not saying it hasn't been done, or I haven't been playing with it. Just things to consider before pouring money into an older frame project.
Don't read that as discouragement, though. Some Lefty mods on non-Cannondale frames look absolutely spectacular. Just make sure get the an enjoyable ride out of it.
appreciate the info. i lived in the 26" world...and 650B and 29" is a whole new universe.