Hi Cornish,
Based on E/EF-Series Disk Drive site it list the following part numbers:
E-X4036B-R6 - Same disk, but different drive canisters for a different platform
E-X4038B-R6 - Part you mention
E-X4091A - Same disk, but different drive canisters for a different platform
If you are looking for the alternate part that we ship it is SP-4038B-R6.
Let me know if that helps
Thanks
Team NetApp