From what I see, both the 3220/4350 support FC targets.SO, I am not sure about your comment. I use SAN on my nodes.
You can set up one or more vServers (very similar, but slightly different than a vFiler)
to serve FC/iSCSI LUNS and/or NFS/CIFS traffic
In my case (I am a partner and did my own Professional Services work),
I was able to procure a new FAS3170 pair with a TON of disks
(enough to split betwixt 4 other heads!)
I staged my data one or a few volume(s) at a time.
WIth tools, I was able to use the equivalent of SnapMirror
to send traffic to the new Clustered ONTAP. After the data
was migrated we updated maps and pointed to the new locations.
It took about three months, but I had something like 400 volumes to move.
Got it done.
Your milage will vary. Bottom line, it would likely be best to secure
the use of NetApp Professional Services to aid in the migration effort
if you have a large/complicated installation.