To drift off topic, yet again,
The 803cc BMC A Series engine (Used in the Morris Minor after the 918 cc Morris side valve, and the A30 ) was replaced in late 1956, by the 945 cc engine to power the Minor 1000 and the A35.
There were features, such as the dashboard layoiut on the Minor 1000 and the gutters on the A35 that distinguished them from their predecessors. Our 1955 Minor was 803 cc but had the 1000 type dash. Sadly it did not have the better gearbox that mated with the larger engine..
The GPO restrictor was just a steel plate inserted between the SU carburrettor and the inlet manifold.
On the earlier and larger Morris Commercial vans a Solex Governor carburettor was used. In this the throttle plate was not directly controlled by the throttle linkage, but by a spring loaded device which sensed induction vacuum and limited speed by preventing it going below a preset value.
Supposedly, it could be partially overridden by using the choke to increase the vacuum, at the expense of fuel consumption and black smoke!
Howard