how to convert Sabatti Rover 870 floor plate to magazine

[Boltcarrier]

i saw that there are magazines for the Sabatti Rover 870 .308 cal for sale but never a gun with the magazine for sale, ie all Sabatti Rover 870s seem to be with floor plates. so when i saw magazines for this rifle i presume that you can convert the floor plate to magazine. but i couldn't find any instructions to do it.

please help.

 

[kg]

Call Marstar. they've had both versions.