Rotating at the splines affects the L/R positioning of the shift lever, and sliding along the splines (within the range of the notches in the shafts) affects fore and aft positioning of the shift lever. "Fine tuning" is done at the turnbuckle.
The turnbuckle is also used to lengthen or shorten the shift shaft if you run out of "notch" adjustment at the u-joint.
Since yours seems to be pretty close, make the L/R adjustment at the turnbuckle. Then, if you need fore/aft adjustment, make that at the u-joint by loosening the pinch bolt.
John
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