That's a sweet setup...a buddy of mine has the same only with a SureFire fore end and 2 shot mag extension. 870 Super Mags are awsome and fun to shoot!
Nice vid...good choice, I have one as well but a super mag (can shoot 2 3/4", 3", and 3 1/2" shells). If you don't already know, instead of drilling and tapping the receiver to put a picatinny rail, get the Mesa Tactical picatinny rail with carrier yoke. I got mine at Opsgear, you should check it...
This was shot on the Lakeshore in Etobicoke, Ontario between Kipling and Long Branch