Benelli makes Left Handed models of their Montefeltro and Super Black Eagle guns. I believe that the PG and shorter barrels will fit on the Super Black Eagle, and you would get the advatnage of 3.5" shells if you wanted them.
I am not sure if the Montefeltro is interchangable with the tactical accessories for the M1.
I would think that the safety can be reversed on the M1/M3 though. What the safety does is cause a post to be pushed up into the trigger group, effectively keeping it from operating. The cylinder that is the "safety button" should be able to be removed and reversed by any Benelli authorized smith, psuhing the button will still cause the post to be "ramped" up into the trigger group.
Consult a qualified smith on this, and don't try it yourself...