The receiver is D&Td for the standard H&R/Weaver base, you can get a Williams WGRS sight from H&R for $18 and shipping, and a ghost ring aperture from Williams or Midway for it, the sight mounts in the two rear holes. You can also just use the WGRS without an aperture, the aperture carrier works just like a ghost ring. See Peep and Firesights in the FAQs and Help sticky in the Centerfire forum.
Tim