Have you seen one more upgrade for your Magpul forend? It enables you to install Surefire Scout Light or other Picatinny-mountable light: http://tinyurl.com/bzxedrw
BTW if you are in Central TX and need your 870 worked on please check out Wade Parham http://www.Parhamcustomguns.com
We test fired my gun and found it was not feeding properly and he was able to identify and correct the issue ASAP.
After a little bit of grinding and polishing by Wade my 870 was racking and shooting beyond anything I expected!