My H&R Pardner Pump Protector has a receiver made in China, but a barrel made in USA.
It took a Remington Model 870 stock, but the older butt screw length. The newer one [off my 2015 870] had a screw hole and bolt that didn't work well.
I also have an 870 Riot gun forend attached.
There are directions on making an adapter for converting the system to a standard 870 barrel.
The inside was VERY rough- but a lot of work on my part slicked it up to be more slick than my factory 870.
The Shotgun receiver has a rear 'hump' that is more like an Auto-5 than an 870, but I like that about it.
I believe about all the internal parts in the action are interchangeable- but they might require a tad of work. I have just slicked up my parts- not replaced them.
I have the 12g Protector, and am seriously considering the 20g pump, as I use 20g a LOT less, and I like the idea of spending less than $200 for it, compared to $350+ for an 870.
I have nothing against Mossberg, but own no Mossberg shotguns. I just prefer trigger-group mounted safeties, as that is what my other pump shotguns have.
The Maverick may cost about as much [or less], and could be lighter. However, I am not lugging it through fields for hours- so that isn't an issue: recoil absorption is.