You are correct, the No. 7 does have a replacement rear sight. The original is about 1/3rd shorter, windage adjustable and has a 3/4 inch cup peep sight(see "The Lee-Enfield" pages 504 to 508, or "The Lee-Enfield Story" pages 438 to442).
The No. 8 was made by BSA specifically for New Zealand, and they only made around 2,000.