Mine are 11-rib. 31 42 1 234 908 on my invoice dated 17 April '92. That is the same part number Hucky has for the 11-rib.
I don't think I would want 13 ribs, as there would be too much material and they would restrict the full compression travel of the forks, as was pointed out to me by Duane.
I don't know who advised me on which boot to put on in 1992.
I had the bottom of the boots pulled "just over" the tops of the sliders, and Duane said to pull them down as far as they would go, to allow more free space.

They are pulled down, in this picture:
