If you look on page 252 on Roger C Rule's "The Riflemans Rifle Winchester's model 70 1936-1963" book there is a picture of a Standard Model 70 that is a Special order 4 with "Special order feature: Quick Detachable Swivels on Standard Rifle"...... so it certainly could of been ordered that way or been clean up....
This model 70 built 1953 so not parts clean up and also block in rear site base too as it looks like factory done too. This rifle is/was somewhat puzzling with these features as unknown if re-stocked or special order as its overall condition is 98% metal and 97% wood.