Just to close the loop, I couldn't get the DNS-320 to read the drives from my old DNS-323 "as is", even though they were JBOD and not RAID. Since I'd already recovered a good number of files from the drives using R-Studio, I just went ahead and reformatted them so I'd have a functional NAS device again. It's a good lesson to learn, however, to have a backup of your backup (grin)!
Fortunately, we didn't store critical files on the device, and we used it mostly to share files between computers on the network, meaning most of them were downloaded from the NAS to someone else's computer. Since I don't know if the restored files and folders represent all of the ones that were actually on the drives, ignorance is bliss!
Thanks to JavaLawyer, who's been a great help throughout this process!
The disks are actually setup differently which makes them none interchangeable.
The most obvious differenence is DNS323 main data is in /mnt/HD_a2 whereas DNS320 it is /mnt/HD/HD_a2
The way I rescued mine (none JBOD) was Linux boot CD and bit of looking to get appropiate mount command for both windows and DNS323 disk.