I found this video on YouTube to be incredibly helpful when trying to fix shifting issues in my Vanagon. The poster uses a piece of wood cut down to 23mm to make the spacer.
I didn't have a piece of wood, but I did have a 3d printer.
The piece is designed to be tall enough to sit in the bottom of the shift box and run all the way up to the linkage. This makes it way easier to work with when you don't have someone to help you hold tension on the shifter. The “23” is there just so you know which direction is the correct way to face out since the two dimensions are somewhat close.
The author marked this model as their own original creation.