How to add rear sight to Remington 870

[samuelrice]

Hello,
I was invited to a hunting trip, and I only have a Remington 870 with a bead sight. I plan to use rifled slugs, but the bead sight isn't adequate. Does anyone know how I can add a rear sight to work with the bead? The gun is drilled and tapped and has a top rail.

Any advice would be appreciated!