I believe that I may be making progress in terms of sourcing the conversion kit. I was given a number of a guy called Anthony in England who bought all the remaining parts from 4 Wheel Traction Ltd when they closed down in the 80s. I got in contact with Anthony today and there is hope of getting the conversion kit. Unfortunately he has not got the transfer case to suit my tractor as he explained that the splined shafts in the early Massey ferguson tractors contained, what is know in the industry as a core splined shaft.
The later models contains a fine splined shaft. But he did say that he is waiting on the core splined transfer case to come in, so I will be keeping in contact with him. One thing I must do is to look at the different shafts and splines to see what the differences are, then this might point me in the right direction to where I could possibly carry out the conversion.