Agree with Vishnu and Victor, only restore with a backup same version.
Possible steps to consider:
1. Create a backup from your current configuration
2. Export your certificates from the current nodes as PKCS12, it have the private key in it.
3. Install a new CPPM node with the same major and minor version of your current cluster
4. Join the new node as subscriber to the current node.
5. After the database are synced, drop the subscriber with keeping the databases.
6. Now you have a standalone copy of your current cluster
7. Upgrade the new node in required steps to the lastest stable release (i should go for 6.8.x those days.
8. Install a second node if you need redundancy. (off course you will)
9. Join the second node as subscriber.
(for license migration call tac support)