Dennis,
The bottom of the notch should be parallel to the slot and slightly above it. From the photo, next to the bottom, It looks like you have enough material in the hook to do this. If you hold the rear foot tightly in the base, and reach into the slot with a scribe, you can scribe a line on the hook that is parallel to the slot. Then you can carefully file to the line, but leave it slightly above the slot. The bottom of the "slider" shows clearly how it was fit to the original mount. It looks like the original hooks were a little more above the slot than yours will be. This is evidenced by the amount of material filled off the bottom ( in two places)of the slider. You should study the relationships carefully and take whatever measurements you can, but it looks like you will need to make a new "slider". Things are so close, that I might be wrong about that. If you have to make a new "slider", you should not have to make the whole thing, just the flat "bar" that slides back and forth inside the slot. If you look very carefully, maybe with magnification, you might be able to find the screw that holds it to the thumbpiece. This screw is normally filed and polished and finished to the point that it is hard to find. You might have to remove the bluing to see it, and you might not be able to turn it out, having to resort to drilling it out. Once out, it can be replaced with one that has enough material to fit it up. If you have to drill it out, you would naturally have to make a new screw. If you have other questions, I will try to answer them.
Mike
