You do not need to ruin the rifle by drilling it. Find a piece of pipe the same internal diameter as the outside of diam of Cadet cylinder. Cut out a rectangular section out of the pipe the correct width of the sight mount clamps x the length you want. File a slight angle along the long sides of the steel to give you about 45 degree clamp for the mounts. Blue piece with G96 gun blue paste. Glue in position on rifle with Tiger Seal polyurethane. Leave for 24 hours and it will not move, but with a bit of effort you can get it off in future if you want to return the rifle to original.Clean any residue off with cellulose thinners.

Baz