Having never tried it, I don't know 100% if the M1 and M2 barrels are interchangeable. If I'm not mistaken though, the M2 is a variation of the M1 by incorporating the comfortech stock, "Crio" barrel and a new trigger guard design. Otherwise, they appear to be the same dimensionally and mechanically.
Might want to give Benelli customer service a call before dropping the coin on the M2 barrel... 301-283-6981.
Don't be surprised if you're on hold for a while.