Futaba says not to change crystals across bands. I know almost all the other radio mfr's don't have that restriction and they're fine. But the difference in range or signal rejection might mean the difference between recovering from a glitch and loosing a plane, so IMHO it's not worth it. See if you can get someone at your club to swap you a low band for a high band receiver, or at the worst send it back to Futaba and let them retune it.

Andy