With all due respect, the rear sight is the same as on the 1863 Springfield. However the 1861 Special Model is correct as the real difference are in the shape of bolster on the barrel, the shallow notch for the bolster in the lock plate, and the hammer which is unique to the 1861 Special Model. If anything can be read on the lock plate it will be either: Colt; LG&Y, or Amoskeag, all of which had contracts for the 1861 Special Model Musket.
J.