Got it in one Graham,
I think only one or two were built,(largely experimental), by Moore Road Machinery. It was based on the Challenger 3.
From what I can gather the clutch, which was basicaly a 16 inch foot opperated lorry clutch was the main problem with the "3s".
Moores who were the Auatrailian agents modified them for their market by fitting a "Fluid Flywheel" transmission with only limited success.
The Challenger 4 used the same Rockwell overcentre hand clutch as the IH TD18 & 20 which was pretty reliable and was used in the later 33s too, but apparently Moores also fitted "Fluid Flywheels" to some of these.
Fred