I have an 870, and it's an awesome turkey gun.

I think that over the summer I'm going to save up and buy a 24" barrel for it, and I'm going to go ahead and spring for the one with a cantelever scope mount. That way I can mount either a red dot or very low fixed power scope on it, and it will remain zeroed with the barrel even when I swap out. I'm planning to do the same with a rifled barrel, too.

You can drill and tap a mount on the receiver, but if you do that then every time you take the gun apart to clean it or swap barrels or even just bump it real good the barrel will shift slightly and you'll lose your zero. If you're going to do that, then you can pin the barrel, but that takes a gunsmith and the right equipment. Personally, I think the cantelever idea is the better idea, since it means I can use whatever barrel I want and my turkey scope stays zeroed.