This is a link from another style of taper turning attachment but the principle is the same on all of them where the cross slide lead screw is disengaged and the cut put on with the compound slide.
Sadly this one was in the acid cupboard I mentioned but it will clean up ok.

The 2 short dowels at one end locate in one of the T slots and the holes take T bolts.
The bar engages with hole in the part that slides along the rail on the taper turning attachment. A bar is used to allow some height variation as the parts are moved about. This one uses 2 dowels as a guide in the adjustment slot so that it can be adjusted and tightened without turning. These stop short of a washer under the clamp which is on top.
John
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