Also, Springfield Sporters seems to be a good source of parts.
I'd leave the rear sight alone for now. Don't worry w/ volley sight fore end and other parts, due to your '27 vintage barrel its entirely OK to leave those bits off.
Pattern14, I believe the reference to a "pinned" rear sight is about formerly windage adjustable sights that have had the adjustment knob and cross shaft cut off flush, w/ the remainder locked in place by a vertical pin. The elevation adjustment was not affected.