[De@dMe@t]

merge all \ flatten select the center section with magic wand tollerance 0, ctrl+shift+v to invert selection ctrl+c then ctrl+v you have periscope with no alpha just a hole in the middle. create a new background 1024x1024 copy the no alpha layer onto the new background, ie paste as new layer. move to bottom, overlay your new marks by copy and pasting, if you have to copy and paste the origional scope on top to use as a guide for line\marks & then delete it afterwards thats fine,just dont forget to delete it. once finished select merge visible, export as png, psp, tga, i always do 3 incase it messes up while exporting. if you want it as a dds convert the png to dds.

failing that if you have a steady hand and lots of patience try the background eraser.