The exe is an installer. If you get just that and run it, it'll create a new 246 directory with the update zip, the boot.img, and the recovery.img. You would then put the update zip on your sdcard-ext, reboot into recovery, flash it, wipe the cache, reboot, and you're done. Those already on 905 have it easy....the updates are DESIGNED for 905. It's only when you're on an update and you need to move forward that the HoB is required.
Ok...that makes sense thanks.
I am confused by the other poster that mention he would rather use the HOB as a safety net, how is using the HOB from 905 safer than using the sdcard-ext?