Numeric racing may have a solution, or Function First may sell an extra little arm for that for 5 speed, maybe they could sell just the arm (or the ends to upgrade the arm). In both cases I would call and let them know that you have one of the early cars with the smaller ball end.
Numeric:
https://store.numericracing.com/collections/transmission/products/shift-rod-linkage
Function First:
FUNCTION-FIRST > Shifter Cable Ends