I can't find an actual .flash file - I download the fwpkg file, if I extract that I have a .bin file... I've uploaded the .bin to the iLO repository and then added the install to the queue. While powered off it did actually start installing (more than I've ever got it to do before) - it made it to about 75% then aborted:
Firmware Update
The last attempt to update or upload firmware was not successful. Make sure you are using a valid, signed flash file and try again. If you are attempting to install a component, first upload it to the iLO Repository then add it to the Installation Queue.
Clicking on the job in the queue:
Name: Update-SPS
Command: Apply update
Component name: Server Platform Services (SPS) Firmware
File name: SPSGen10_04.01.04.381.signed.bin
State: Exception
Result: The update failed with a component specific error. Retry the update after fixing the component error.
Installable by: iLO
Maintenance Window: None specified
Start Time: N/A
Expiration: Never
Update Recovery Set? No
Created by user with Recovery Set privilege? Yes