The idea came from Selene in Italy after WW2 when they needed extra traction for ploughing heavy clay soils. Selene used surplus front axles off the GMC 6x6 CCKW trucks which had been left in Europe by the US Army.
The first tractors converted with the 1945-51 Fordson E27N Majors. The project was very successful, and they went on to convert Ferguson T20 & Ford 9N/2N tractors using Jeep front axles.
The CCKW front axles were made by two different companies and were known as "banjo" and as "split" by GMC & the army. The one side of the axle was shortened to make them the correct width for use on tractors.
The name chosen by Selene for these conversions was MANUAL. They supplied kits for many makes of tractors in Europe. The CCKW axles was used on larger tractors, and the Dodge WC-51 axle for smaller tractors. Selene supplied them all over Europe.
In 1954 the British crawler manufacturer Roadless Traction obtained the licence to sell the Manual 4wd axles & transfer boxes in Britain, Canada and the USA to fit only to Fordson Diesel Major tractors.
Initially kits were bought in from Selene and fitted to tractors - later Roadless were able to manufacture the transfer boxes and to purchase the axles from surplus stocks dirrect, paying Selene a royalty for each tractor converted. This arrangement continued for many years into the Ford 5000 tractors.
Roadless also sold the Fordson Dexta, Super Dexta and Ford 3000 fitted with Selene axles based on the Dodge 51 axle & transfer boxes . ALL these came into Britain as complete kits from Selene.
I'll post some photos of the 1963 Roadless 6/4 tractor fitted with 6 cylinder engine in another thread.