Here's a link to the 2009 USAW Guide to Wrestling. On pg. 45, the procedures for the Greco-Roman Ordered hold are laid out.
There is no "ball grab" (we like to call it random draw ) in GR, only FS.
There is a 30-second rest between periods. You must win 2 out of 3 periods to win the bout.
A fall will always determine the bout, at any point during the match. (pin=win)
The only other majour change you need to be aware of is the step-out. If you step out of bounds, your opponent will be awarded a point. This does not apply however, if you happen to step out of bounds, while you successfully (i.e., score points) attempt a technique that you initiated in-bounds.