UPDATE UPDATE UPDATE!!!!!!
I picked up a pair of the earlier style chrome base type, with the plastic cover. And well, THE SPLINE DIDN'T FIT!!! But the good news is, the screw did!!
So I was able to get it to work. The spline has the correct number of teeth- 12, and the major diameter is correct. It's the minor diameter (the ID over the teeth) that is too small. So I drilled it out. Use a 27/64" drill bit, and drill down to the shoulder at the bottom of the spline. Then use a 7/16" bit and drill about 3/16" down into the spline. Last step- take a tiny triangular file and clean up the burrs covering the splines, and sharpen them while you're at it. Takes a few test fits and more filing, but it'll eventually fit.
I like it. Picture below-
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