Just for the heck of it I pulled out my model 67 no dash, 4", with a parkerized rear sight and it's 2.75" long like the one in your photo.

And, just like rbmac52 said the front edge of my sight is about 1/4" back from the barrel/frame joint. As AverageEd said, the screw that fastens the leaf down to the frame is located right above the forcing cone.

Good information; you learn something new everyday.

Bill