I don't have the capacity figures right here, but
ISTR that a raw 9762
drive (on an SMD controller) was around 80MB, but as DEC used it in the
RM02/RM03 it was an effective 67MB. I know that the 160MB SMD Fuji drive
I have emulates two RM03s, at 67B each. There may be a similar thing
going on with the 9766 vs the RM05.
I recommend the excellent document on DEC disks at Phil Budne's site:
http://www.ultimate.com/phil/pdp10/