My contact man advises me as follows:
The production Start Dates and S/Nos for the UK built MF 30,40,50 Industrial Tractors at Banner Lane were :
MF 30 1969 First S/No 900001
MF 40 1970 First S/No 838162
MF 50 1970 First S/No 822904
He doesn't have the dates for US built machines but surely they must be about the same year - possibly only a year earlier at most?