Here is the original cross slide all torn apart.
The above photo shows the stock mounting bolt. It was lightly pressed with a reference pin into the slide. The bolt hole in the slide needs to be modified to accept the new base.
Here is the slide, base, post and bolt ready for assembly. The smaller hole at the top of the slide was a pocket for a spring loaded pin that was used for indexing on the stock post. If I ever modify this quick change I think I will use that hole somehow. Maybe press a pin through the hole into the base to help tie the assembly together even more. I have noticed a big improvement in the tool post after the mod. I held off on the heat treat of the post until I tried it out, in the event I had to modify it a bit. I can think of a few changes that would be good but it works well enough for now.