As always, photos will go a long way to helping us help you. One concern I have right away, since you suspect the fork is not original, is whether the frame has been damaged, as well as the original, discarded fork, due to a crash. Photos exactly perpendicular to the plane of the frame will help rule this in or out, as well as close-ups of the down tube and top tube near the head tube. Check especially for dimples in the tubes, and cracks in the paint in these areas.