It sounds like you don't have the hand guards removed from the pump slide carrier
- Remove the two screws below the hand guard and split it open to remove it from the carrier. (Only one side will come off.)
-At the bottom of the carrier you will see one single screw. Remove it to release the opposite side. (This should give you access to the 'underneath' part and the two rods connected on the slide.
Now you can access the two screws on the part forward of the magizine that is underneath handguard normally as well as the rod tops on the carrier assembly. That should give you the room you need to work.
Let us know if that worked. Sorry abut the picture quality, I only have a crappy camera phone at the moment.