Should be easy to do.
Your search appliance provides the ability to export all configuration information in a single file and import it back into the system. The exported file serves as a reliable backup of the configuration and can be used to replicate the same configuration across multiple appliances
So login to the GSA Admin interface, go to Administration --> Import / Export and export your config file and then import it into the new box and you should be good to go.
I've not done this myself, since we only have one GSA, but this seems to be exactly what you want / need.
Hth.
Tim Stevens