When I began to investigate why they might not work, I found the answer pretty quickly as I grabbed a bundle of unconnected harness cables from below the carburetor. The real challenge was then finding that the harness connections bore no resemblance to the connections presented on the wiper motor.
The correct motor provides two-speed operation and 'reverse park'. The latter means when you switch it off, the motor is immediately thrown into reverse, tapping into an ignition-switched supply on the harness that is then interrupted by contacters on the internal parking finger.
There are fuller descriptions on the web. And the most useful, including a wiring diagram, I found was here....
In any event I was rescued by Brian, the Gilbern Owners Club's GT Historian, who produced a refurbished DR3 for me. This needed only for me to switch the gear and the 'parking finger' from the original unit and to rework the original harness, restoring the some of the blade connectors and spurs for the associated washers.
And the parking finger (positioned in the lower left of the gear case) determines whether the motor parks on a 'push' or a 'pull', hence where the car the wiper blades park. There is a twiddly knob on the end for fine adjustment.