Unless someone knows something I don't, a Remington 870 barrel is a Remington 870 barrel and doesn't care about the model.
Not quite true. There seem to be a lot of 870 Special Field barrels floating around these days, 21" VR RemChoke barrels IIRC. The SF version has different dimensions than typical 870s and the SF barrels will not fit Wingmasters, Expresses etc as the barrel ring is in a different location.
Other than that, given the same gauge and receiver code, barrels will pretty much interchange with no problems. It's possible to put 3" chambered barrels on 2 3/4" receivers (and vice versa) but that won't make the gun capable of handling 3" shells. And so on...
lpl/nc