Zane (and anyone else who is keeps DEC module lists),
In case anyone is wondering:  
ftp://zane.brouhaha.com/pub/ModuleList.txt
The list is for non-Q-Bus and non-Unibus cards, and it started out as a list
combining all of the PDP-8 card lists that are out there (each of which had
at least some different data).
  I can confirm that the G646 _is_ part of the
H212/MM8-EJ.  You may
 "connect the dots" in the Module List.
 -ethan 
Many thanks!  I just updated it.
                Zane