Dealership number one that is "young" only had books back to 1982 and a fuzzy image in the drawing and no part in stock.
Dealership number 2 had an "experienced" guy that took my verbal description and came back with the correct black plastic part immediately, knowing exactly what it was without looking in the older parts books that dealership number one said they had there at dealership number 2.
Cost = $2.50.
Benefit: More precise shift selection feel. - It seemed OK without, but was more precise with. I would not have thought to look at the linkage otherwise.
I did an engine swap between 2 1972 cars. Neither car had this plastic piece in place. You might want to check your '65 and newer car to see if yours is missing the next time it's up on the rack..... Item will snap in with no tools required.