i currently use a dmt8c for lapping my naniwas
It work very well with dry naniwa stone (very fast and very good job) . I have only a problem : clean dmt is diffucult when I lap naniwa 12k because the fine particles of naniwa12 occlude interstices and them are very diffult to remove
If you lap them under running water it will be easier to clean as not as many particles will be left behind. Also a good brush scrubbing does work well.
I had a picture in my mind then of you rubbing the stone on the ceiling and thinking its a bit heavy, surely that's not easy !! Then I read the rest and gave my head a bang for been a dumb ass