In the early years, Thriftmaster and Loadmaster referred to the size of the truck. After the middle of 1949, Thriftmaster referred to the standard 6-cylinder truck engine (216 or 235, depending on the year), and Loadmaster referred to an optional, usually larger or more-powerful 6 cylinder.
In 1954, a Jobmaster 261 truck engine was added.
In later years (1955 an onwards?), I think the
Trademaster/Taskmaster/Roadmaster/Workmaster names were given for V-8 engines 
