True enough. If you have an existing sight on the rifle then you won't need the through bolt, plunger, plunger spring and through bolt retaining pin.
If you are looking to put an "authentic" (proper manufacturer, etc.) ladder sight on the rifle then you will have to ask someone who is up on the minutia of Enfields. I can't help you there. If you just want a good, high quality authentic ladder sight for shooting then contact Springfield Sporters. I'm not into matching codes and all that stuff. I leave that for the collectors. I just like to shoot!