Okay. I got my MagPul trigger guard and installed it on my "L" series Bushmaster lower. It will work with the Tango Down pistol grip. The TD grip has a duck bill, and the trigger guard will push the duck bill down causing a slight gap between the duck bill and the MagPul trigger guard. But is isn't bad.
There are two options to clean that up. First you can cut the duck bill off the TD grip, which is the easiest mod of the two. Or, second, you can file down the MagPul trigger guard slightly to accomodate the grip. I did this one. I then hit the trigger guard with a little flat black paint to hind the file marks. And since this is hidden under the duck bill it doesn't show at all.
That being said, it might be easier to modify the grip. That way you can interchange grips with no cosmetic issues. And its easier to change out the pistol grip then it is to change out the trigger guard.