dandy,
SRM has mag extensions for 2,3,4, or 6 shells. I think you would have to make your limiter out of a wood dowel or some thing similar.
http://www.surecycle.com/default.asp
dandy,
your gun looks to be a montefeltro with composite/comfort tech stock and forearm.
if your barrel lug looks like this,
http://www.benelli.it/Images/Image_Visualizza.asp?SmallMenu=TRUE&ID=1289&NoDescr=TRUE
it will not accept a mag extension.
G,
below the safety is a spring loaded pin that works against notches in the safety.you have to work with a pick to get around and under the safety and push down on the spring loaded pin.
the safety is reversible.strip the trigger assemby down to the top of the safety,depress the detent below the safety with a slim pick or paper clip,
slide out the safety and reverse it.