The difference between 111-00585 and 111-00586 is that the 111-00586 is the part number that we used for a PCM (motherboard) replacement. The 111-00585 was used for a full headswap that would come with memory and boot media.
If you are looking for a replacement PCM then look at the 111-00586 which is the part used for a standard motherboard replacement.
Hope that helps. Let me know if you have any additional questions.