Newsrail April 1982 records the small-van units as "11, 12 and 20", and coupled to 3RM as of 8 June 1976, and 31RM as of 1 January 1977 [REF].
Separate to the paired units, railmotors 80-92RM consisted of two driving/sitting units, one either side of the power unit that gave its identity to the full consist.