Go out and shoot a few with just the bead. You might be pleasantly suprised. I was. My 21" vent ribbed 870 will put 5 Remington Sluggers center mass on an IDPA target at 75 yds.
If the bead doesnt work , the XS Express sights are a good option without getting too far away from how a shotgun is meant to be shot.
http://www.xssights.com/index.php?nI...&pID=specialty