I also don't understand why it would necessarily stay in sync. Is it
safe to assume that the Apple's crystal and the Carte Blanche crystal
are so close to the same frequency that they would not drift out of sync
in a noticeable amount of time?
You would not want to use the CB's on-board clock. Instead, you would
want
to utilize the FPGA's DCM (digital clock manager, usable as a
frequency
multiplier) to derive your operating clock based on the A2's own 14M.
In this case, you would indeed stay in sync.