It would take about 5 minutes with a dremel. All you need to do is round out the rear of the magazine port to make room for the magazine keeper. It's very obvious if you have a centerfeed stock with the DBM already in it.

Here's a picture of a stagger action in a centerfeed DBM stock. I circled the area that need attention.

[img width=600 height=450]http://i234.photobucket.com/albums/ee269/geargrinder123/S8001244-1.jpg[/img]