S&J has extended charging handles, safeties and bolt release tabs, and a Picatinny rail/sling loop ring for flashlight mounting.
You can get a Carlson's magazine extension from Al's corner store. Its flush fitting, looks awesome and will bring capacity up to the legal five 3" shells (six 2 3/4"shells). Plus I don't think there are many other options available up here. Disassembly is harder tho.
I have these 5 mods myself and really like them all.