Now I get it. That is possibly part of the reason that the bracket got broken. I can imagine that it NEVER worked right so someone muscled the lever trying to get the feed either engaged or disengaged.
How to fix it? Well, from your top photo it appears that the tapped hole for the 8mm (size a guess) set screw is far from center. Fortunately, that looks to be a simple part to make, and nearly as easy to check the one you have. Got a center head for a combination square? If so line up the scale to lie across the middle of the keyway, then scribe a light line acriss the face to where the tapped hole should fall on center. Does it appear to be as far off as it does looking through the hole when its on the shaft?
If the hole in the smaller shaft is off center, much harder to make a new one of those. Be prepared to bring both with you?
How to fix it? Well, from your top photo it appears that the tapped hole for the 8mm (size a guess) set screw is far from center. Fortunately, that looks to be a simple part to make, and nearly as easy to check the one you have. Got a center head for a combination square? If so line up the scale to lie across the middle of the keyway, then scribe a light line acriss the face to where the tapped hole should fall on center. Does it appear to be as far off as it does looking through the hole when its on the shaft?
If the hole in the smaller shaft is off center, much harder to make a new one of those. Be prepared to bring both with you?