I'm not to sure about the construction of the gas system, but if what be2man has posted is true, and it isn't just a barrel swap, that other parts need to move to, it could be a problem.
also do the benelli's have an adjustable gas block? cycling could be an issue if not.
as for bolt face, etc, everything would be good.
I know there was some talk about a 300 AAC barrel swap for the XCR, but I was never able to dredge anything up.
I know rob arms is now making 300 conversions for the short xcrs. maybe they could do a run of long for us...
mind you,IIRC if you are running subsonics, isn't all the powder burned in 9 inches or less?