This is not the official 600 for the 9780, but gives you the exact same effect in essence to you can use the latest OS from the 9700 on your 9780.
Why did I post it? Because it is worth it, it is not just some small version increase, I have tried all the 9780 OSes extensively, including many Hybrids (which didn't go so well btw, Hybrids only decreased my battery life rather than increase it as they claim to say).
Here are the instructions, and please do not skip, or change the order of how you do things:
1) Go to Control Panel, then Programs and Features, or Add/Remove Programs if you are on XP
2) Ensure that you do not have any BlackBerry Device Software on your computer, if you do, uninstall that.
3) To make sure that we do not have any Loader files which were not uninstalled from previous OSes, go to: C:\Program Files (x86)\Common Files\Research In Motion\Shared\Loader Files (if you do not see Program Files (x86) don't worry it means you have a 32 bit Windows, just go to C:\Program Files\Common files\etc... )
4) Delete all the folders WITHIN the Loader Files Folder, so if you find a folder named 9780M_v184.108.40.2064 or something similar, make sure to delete it to ensure we have a clean install for our next OS
5) Install 9780 - 220.127.116.116 (This will be our base OS and its radio will be the only thing we actually install from OS 576, rest are all the 600 JAVA files.
6) Go to: C:\Program Files (x86)\Common Files\Research In Motion\Apploader and delete the file name Vendor.xml in there
7) Download this file >>> Multiupload.com - upload your files to multiple file hosting sites!
8) Extract its content to a location of your choice.
9) You will find a folder named 9780M_v18.104.22.1686_P22.214.171.124 ignore the version number, it actually contains the 600 OS Java files.
10) Copy the Java Folder found in that folder.
11) Go back to C:\Program Files (x86)\Common Files\Research In Motion\Shared\Loader Files and now you will find that you have a Loader files folder with the version of the 576 (the base OS you just installed), go inside it, and DELETE the JAVA Folder there completely. [Only delete the JAVA folder, not the *.alx files which are found near it!]
12) Paste the JAVA folder which you have acquired / copied from the zip file.
13) Shrink your OS if you wish (This is an optional step)
14) Run loader.exe from C:\Program Files (x86)\Common Files\Research In Motion\Apploader as you normally would and start to install your new 126.96.36.1990 OS
Tips: As soon as the installation is done and the restoration have been made, do a battery pull. Then apply the license keys to the apps that you have that are paid (Example: Berry Weather or Meter Berry), after the licenses have all been restored, do another battery pull.
I recommend performing 3 - 5 battery pulls during the first day, and try keeping the battery topped off / fully charged at all times. This will help in running in the battery to give you an accurate reading.
Enjoy your new OS and do not hesitate to ask any questions if you have a query.