4 speed identification

What should the diameter of the retainer be for a 23-spline shaft?

By the way, I found a neat way to count splines (new to me, anyway): Put a light coat of grease, or something that can make a definitive mark on paper, on the outer surface of the splines, then wrap a piece of paper around the shaft. Count the marks. Mine was found to be 23. Definitely not 18.