Look up the Remington 870MCS...the grip is attached and is quickly removeable to attach the shotty as a 'Masterkey' under an AR (You can see the removeable pin in the picture).
And yes, has to be built with a grip to be AOW vs SBS. Mine is a factory built Shotty from Remington.
Ok. Where do I get one?!
It would be really sweet to have that grip for my 1100.