Only the rear site needs to be taken off. Otherwise you won't be able to hold your hopper up. You take out both plastic pieces of the rear site, and then the holes that are empty is where the rear screw goes in for the shroud. [/whatxjsaid]
Directions should explain it all. I sold my flatty, so I don't have the manual. It explained it well enough for me to figure it out, you should be able to