That is a real "Frankenfield" all right. The rear sight is a Model 1903 for the rod-bayonet rifle, probably sold as scrap by Springfield.
Getting the 1917 Enfield bolt to work would be fairly easy as the 1917 bolt is larger and longer, so it could be turned down a bit and a section cut out. Fitting a Spiringfield bolt sleeve would not be too difficult.
The work was probably done by Sedgley as indicated by the circled S on the sight base.