there's enough of them out there!!! Depends on how much money you want to sink into the project, but if you're trying for the "tactical mossberg" look. Why not just invest in either a special purpose 500 or a 590??? http://www.mossberg.com/pcatalog/Specpurp.htm
One major drawback of "tacticalizing" the Mossberg is that the safety is not easily accessed with a pistol-grip buttstock. For that stock arrangement, the Remington 870 is probably the better choice, as the safety is in front of the trigger guard.