I am eliminating the remaining shifter play, it seems my existing shift lever has excess play at the base. I.e. I can lift the lever up / play around the ball socket.
I checked my spares, I have a similar lever from an early 914-4. I looks like the Gearshift Bracket 914 424 019 02 is the same. (Item 1)Click to view attachment My 914-6 has been updated to a sideshifter, but I think this part is original.

Is the simple solution to just replace the plastic bushings?

Yes. Same

Check the ball socket for cracking...mine broke, allowing the shift lever to be pushed up and out of the socket (tail shift linkage).

2,6,7,8.

The shifter bases #1 do wear out on the underside.

After you disassemble it and clean it thoroughly look around the area where the shift lever ball goes through the metal housing.

If it is heavily worn or scored its nearly impossible to repair since it stamped sheet metal and it will never be right even with new bushings.

NOS ones are floating around, I've bought a couple for 914-6 restorations and its amazing how smooth and tight the shifter is when this is replaced with a new part again.

BTW side shift bases suffer from the exact same wear issues and they are NLA as well.

I may have an extra NOS part for both types if you end up needing one.

Also the side shift base and early 914-4 & 6 bases are not the same. Side shift base has an extra opening at the rear (toward the seat) the allows for access to the bolt connecting the shift rod. If you put an early base on without this "window" you can't connect the shifter to the linkage.