Hello,
Here are the Knowledgebase Articles available for Symantec Endpoint Protection SBE 12.1.3001 (RU3) which would assist you to prepare for this Latest Release.
NOTE: This Article would be updated as and when new Articles in reference to Symantec Endpoint Protection SBE 12.1.3001 (RU3) gets published.
Product Guides
Release Notes and System Requirements for all versions of Symantec Endpoint Protection and Symantec Network Access Control
http://www.symantec.com/docs/TECH163829
Symantec™ Endpoint Protection, Symantec Endpoint Protection Small Business Edition, and Symantec Network Access Control 12.1.3 Release Notes
http://www.symantec.com/docs/DOC6549
System Requirements for Symantec Endpoint Protection, Enterprise and Small Business Editions, and Network Access Control 12.1.2 and 12.1.3
http://www.symantec.com/docs/TECH195325
New fixes and features in Symantec Endpoint Protection 12.1.3
http://www.symantec.com/docs/TECH206828
Upgrading or migrating to Symantec Endpoint Protection 12.1.3 (RU3)
http://www.symantec.com/docs/TECH206823
Symantec™ Endpoint Protection 12.1.3 FIPS 140-2 Deployment Guide
NOTE: You could also search on the Symantec Knowledgebase as well -
http://www.symantec.com/business/support/index?page=landing&key=55357&version=61945&sort=recent
Hope that helps!!