I can confirm the rearsight was intended to be fixed either conventionally over the breech or at the back of the cylinder, with a peep element that appears to be missing in this instance.

There was one at a few Kemptons before it sold around the £200 mark. From memory, it was not quite as nice as this one.

If it were mine, I'd probably start at £295 but be prepared to take a little less.

John