I recently lapped my Ozuku (it was actually very flat). I used a not well worn DMT8C and a not well worn DMT8F.
Both of them have been used frequently for lapping but are still quite agressive. I took my time on the D8F to get rid of all the tiny scratches.
Afterwards I finished the surface with a couple of small hard stones and nagura. This took a lot of time but eventually the whole stone shines and reflects light perfectly.
You can try your Coticule rubbing stone or a small belgian blue after the D8C and work your way up to tomonagura