I have taken off an original many years ago and remember there is a "set screw" that is put in with a flat head screwdriver. After it is tightened there was a "top screw" that went in behind it. I wonder why they did that but I figure it was and early way to keep the first one from backing out???
Both, the set screw and the cover screw can be purchased from most vendors.
If you have to cut the door handle off let me know. I have an original I would let you have just to help you out.
