I haven't worked on a tail shifter in almost 20 years, and thanks to a post on here, I was able to get the linkage working pretty well. That said, it seems like there's a little too much front and back slop in the gizmo on the tail end of the rear shift bar.

How much can I weld it up to improve the front and back slop? Pics to follow

I've often wondered the same thing.
Seems that reducing the play there has got to improve the action.
If the clearance is greater than the thickness of a hacksaw blade consider this.
Saw through the front and rear cross arms of the box then weld back together.
This will reduce the width of the slot by the thickness of the saw blade.
Front/rear action ? same approach.
Perry have you tried a short shifter ? simple improvement on a rear shifter.

You can weld up the wear points on the rear shift rod and on the selector box on the trans shift rod. File down to profile and it really helps to reduce the sloppy play.