I recently did a head swap for a 3040 standalone to a cluster of 3240 heads. The biggest problem was that the 3040 didn't have CF license installed. When the 3240 started to boot off of those disks, it had a conflict. It saw that the chassis was set for cluster mode, but CF was not licensed - then it went into a reboot loop.
I had to go into maintenance mode, change the mode of the new 3240s to NON-HA mode, boot them with the disks that came from the 3040, and then license CF and then go back into maintenance mode to change the mode back to Clustered mode.
This would have been a lot easier had I gotten a CF license to put on the 3040 ahead of time... or easier if I had anticipated it up front.