In addition of that, you need to take a look of this document "Clustered Data ONTAP Storage Platform Mixing Rules" that is located at field portal. https://library.netapp.com/ecm/ecm_get_file/ECMP1644424
After validation, if you can mix your controllers, you should upgrade your old cluster to 8.3 (to have both in same Data ONTP version) and then join the new and clean hardware to the existing cluster, if you already have data en the new cluster you will need to move your data, wipe the cluster and then join the new hardware to the existing cluster. And you can use your existing switches CN1610 (remember that you need 2) for intercluster conectivity if you will have a 4 nodes cluster.
hope that helps