870 barrels will NOT FIT. I can 100% guarantee you that. The mag tube is a different length.
To be honest, I wouldn't bother putting ANY accessories into that pig. Mag follower, sure, rifle sights - forget it! It was hands down the WORST 870 'clone' I ever owned. And I've owned a LOT. The receiver has this weird hump near the stock, and the fit/finish was freeking terrible. Tons of sharp edges, and clunky action. Brutal.
You are MUCH better off to spend the extra $50 or so and get an HP9-1 or a Dominion Arms Grizzly. The Homeland Security ones are poo. Plain and simple.