I have received several updates from J.R. and will be publishing them in the nearest time. And first upgrades are Remington factory +3 mag extension, an S&J bayonet mount and an Ontario M7 bayonet.

Remington 870 Bayonet Mount

Remington 870 Bayonet Mount

The S&J bayo mount is well built and fits the Remington 870 and the M7 very nice.
From TacticalShotgunner.com

The Ontario M7 bayonet is made well and the blade is coated very well and also includes a very nice sheath.
From MidwayUSA

J.R. thank you very much for sharing your photos and experience! Tomorrow I will post information about other upgrades.

Related Post:

Magazine Extensions for Remington 870 Shotgun (Nordic Components, Choate, TacStar, Remington, ATI)