You should set the property as a system level Java property when you start JBoss - it's not a standard GemFire property that would go in gemfire.properties.
Regarding the versioning - you should find the correct version of the Modules bundled with the 7.0 distribution. Prior to 7.0, this was a separate download. Unfortunately, once you download an eval copy, you can't download any other versions of that component - annoying yes. I'll see if I can find out what to do about it.
--Jens