The history of Leyland becomes rather complex after 1968, but until then it was rather more straightforward. Leyland Motors Limited formed in 1896 and became defunct in 1968 when it became British Leyland Motor Corporation after a merger with British Motor Holdings.
In 1986 the name changed again to Rover Group. Out of the 1970s restructuring came Leyland Cars (later named BL Cars) and Leyland Truck and Bus. The latter company became the biggest manufacturer in Great Britain, producing around 38,000 trucks, 19,000 tractors and 8000 buses per year.
After Sir Michael Edwards became chief executive in 1977 Leyland Cars was split into Austin Morris and Jaguar Rover Triumph. In 1978 BL Commercial Vehicles (BLCV) was created which included the following companies; Leyland Vehicles Limited (who produced the trucks, buses and tractors), Alvis Limited for the military vehicles, Coventry Climax for forklifts and specialist engines and Self-Changing Gears for heavy duty transmissions.
BLCV and Land Rover Group eventually merged to become Land Rover Leyland.
Anyway, enough of all this, it's too early in the morning. My guess is that what you really came for was to look at some old trucks, so let's do just that!
Leyland advertisement from September 1962
Leyland 90 CWT/GVW sales brochure from January 1965
Leyland Chieftain brochure from the 1970s
Leyland EA Van 350, 420 and 440 brochure published in November 1975
The Leyland Terrier (1980s) - "Drive it on a car licence" . This brochure covered the 650, 738, 850 and 950 models.