Series I (1948-1958)

The original Series I had an 80" wheelbase and a 1.6-liter displacement.  In 1952 the engine displacement increased to 2.0 liters.  In 1954, the wheelbase was extended to 86" and a 107" wheelbase pickup model was added.  In 1956, the wheelbase changed again to 88" and to 109", and a 2.0-liter diesel engine was offered as an option. 







 

Series II  - Early (1958 thru 1960) 

More power and a new body style distinguished the Series II from its rough-and-ready predecessor. The alteration from a flat fender treatment to a curved look is the only major styling change here. The new body style included sill panels to hide the chassis and the exhaust. The engine was bumped up to a more powerful 2.25 liters, while the wheelbase options remained at 88" and 109".
A Station Wagon version was introduced (the first SUV?) sporting a full hard top with tropical roof, sliding windows, Alpine glass, roof vent, rear door & full interior trim.
 
Clues:
Look for a steel front grille with three holes for airflow and chrome rings around the headlamps.
 

Series IIA  - Late (1961 to early 1971)

Series IIA's are often referred to as "early" or "late"...the fall of 1967 being the dividing line.  The big change involved the polarity of the electric system and a centrally located wiper mounted on the dash. 

Clues:
1967 "late" – single wiper motor is added to center of the dash.
1969 - headlights moved from the center radiator grille to the wings and the
sill panels narrowed from 5" to 3".

"Transitional" IIA: Three holes for airflow and an almost rectangular steel grille that looks like an upside-down "T".

Late Series IIA: Three holes for airflow and a large steel grille that looks like a fat "+" sign.
 

Series III (late 1971 to 1984)

To keep the owners guessing, the Series IIA became the Series III in the fall of 1971, with some "transitional" alterations along the way. 
  
The new Series III sported a revised fascia with a modern black plastic safety dash. The instruments were moved in front of the driver, and a fully synchronized gearbox was introduced.

Clues:
Series III - a plastic radiator grille and dash.

http://www.roverparts.com/How_to_Identify_Rover.cfm