I don't know what kind of stock you have laying around or if you also have a mill but since I don't have any key way broaches(yet!) and the more I look at that gear for the motor and your descriptions I'd do a semi major rework. The inner dia. Should not be tapered unless the shaft was tapered. Along with that crude key way and the suspect motor mess it all points to some serious jury riggin'. If you have the stock(and there's room) I'd bore the gear out large enough to make a new sleeve for the gear that has a shoulder on it and weld it to the gear(unless it's brass or something other than steel). That way you can bypass the key way fitments and go with two set screws. The way I do these kind of set screws that are expected to replace a key way is once I know right where they are supposed to be tighten them down so they leave a mark on the shaft and then drill the shaft 1/16" with the same size drill in those spots giving the set screws a recess to bite into. They can't slip that way, but it has to be done last because it's tough to relocate. More 2c poking around in the dark.
That spacer is the first useful thing I have turned on my metal lathe. I am a rookie with a metal lathe my only instruction has been from utube videos.
I found out that there is a taper to the inner diameter of the old gear. The first spacer I turned was loose on one end. The second spacer will need hammered on, and I have to cut a keyway and add set screws? There are three different shaft locking mechanisms between the new and the old. Any idea on which I should use or give preference to?