Eu instalaria como um novo Mac e usaria o Assistente de Migração. A partir do site de suporte da Apple :
Open Migration Assistant, click Continue, then follow the onscreen instructions to transfer info from a Time Machine backup or other disk.
Select the disk, then select what to transfer.
Apps: Select the Applications checkbox. Incompatible apps or apps with newer versions already installed may not be transferred or may not be usable.
Computer settings: Select the Computer & Network Settings checkbox.
Your desktop picture, network settings, and more will be transferred.To begin the transfer, click Continue.