Actually, 4 motors plus 3 trailers, they ran as 7 car trains.
Got a few options:
Singles: M or CM
Pairs: M-D or M-M
Units: M-T-M or M-T-D or M-G-D
Blocks: M-T-T-M or M-T-D-M or M-D-M-D
Sets could be any combination of Swingdoor, Tait (clerestory) and Tait (curved roof).
Traditionally, they would run in Unit+Block sets in peak hours, with the Unit detached and left in Jolimont yard in offpeak. At Easter and Christmas, times of high county traffic and low suburban traffic, the G cars would be removed from the Units and shifted to country service. In later years some double-block sets would run to Frankston and a few other lines, which had platform extensions for eight-car trains.
Single M cars, 470-473, would be used for shuttles to Hurstbridge and Alamein among others. CM cars 1-5 and 10-15 were parcels vans, though 3CM and 10CM were also used for overhead inspection trains, and 14CM/15CM were very late conversions. Also, 113M and 156M were used as shunters at Jolimont yard.
Double M cars only ran occasionally; usually including one if not two of 1, 8, 15, 46, 65, 78M. These swingdoors had upgraded motors, and trains were often formed as M-M-(x)-(x), where each (x) represents two or three country passenger cars - i.e. W or PL cars, and a van. The train would run to either Frankston or Lilydale, then the Motors would return as a 2-car set. The two country sets would be split, then loco-hauled to Mornington/Stony Point, or Healesville/Warburton. This practice ceased around the mid 1940's IIRC.
There was also the short-lived Boat Train; from 1936 to 1939, it was an M-D-M-T-T-M set that ran to meet ships at Port Melbourne.
Remaining stock - Swingdoor:
10, 12, 13CM
8, 107, 113, 137, 156M
Remaining stock - Tait:
267, 317, 327, 381, 427, 470M
Note very few of the above are operational. Most are at Elecrail or the ARHS museum; 98G is carrying passengers at Mornington.