If you do try that route, please post back and let us know how everything turns out. 
I am considering it... still trying to understand what's involved with ALT-F roll back and plan for recover if needed. Steps;
1. Put seagate 3TB (back) into USB enclosure.
2. Copy contents of 1TB in DNS-321 to seagate 3TB via usb to computer on network, backup most important files on additional external 320GB drive.
3. Install ALT-F with existing 1TB drive.
4. Get ALT-F working with existing 1TB drive
5. Copy original contents of 1TB drive back into network
6. Install seagate 3TB using ALT-F
Then again newegg just gave me a 20% off coupon so a 2 TB WD Green drive seems like an easier option and keep the 3TB as USB drive possibly on network router.