From the research I've done the picitanny rail is the issue, the 870 Remington I found on you tube is the only one I saw similar to what your trying to do but I'm not a shotgun expert so hopefully someone else here knows better than me. I just looked around youtube and tried to find so info with out much success.......
Concealed 27
Right on I've been scouring Google images and links to their pages tedious lol..I was also looking at mossy's kit for the 500/590 it connects directly not by pica tinny but it's Xspensive.