Hi Tom
ENV differential units were fitted to some of the larger upmarket Saloons of the 1940s and 1950s.
I believe 1950s Daimler used 3.9 & 4.3 ENV units. Caution many of the larger heavier Saloons used ratios of 4.5 even 4.7 & 4.9, one person who could throw some light on the subject is Mike Mansergh, in Workington, Cumbria. suggest you email him direct on...
mike.mansergh@bt.com
If you find a source of supply of either complete units or new old stock parts please keep us all informed as these units are as rare as hens teeth. Good Luck !
Keith L Lessiter