GeeTeeNZ

No, not exactly.  the 2 drives in question JLLP & 43DF (those are the last 4 chars of serial)  in reality are 4TB & 6TB respectively. They were only reported by unraid as 2.2TB because of the old SATA ports on the Z800 I connected them to. 
 
I have spent the last three hours changing the physical positions of the drives, inserting them individually, basically every possible configuration a number of times. I changed the ports they connected to, with no success. What was strange is that the Logical drive position (e.g., Disk 5 or Disk 6) would change depending upon which solitary drive I had inserted. 
 
So, in the end,  I said f@#k it and used the New Config tool again, reset the configuration, and started the array. All drives are now reported in their correct positions and sizes, and Parity is being recomputed. From the quick check I have made all data seems intact. 
 
I don't know how to explain the bizarre behaviour that Unraid has displayed. 
 
In any case, your comment about changing back the drive positions started the recovery process I guess. Thanks for that. I'll put some money on your beer account later in the week when I get paid. 
 
Cheers,
GT