What year is a Massey Ferguson FE 35 serial number SDF140043?

The 'FE 35' was built in Coventry, England.

Your serial number deciphered:

S = Standard Chassis (as opposed to row crop, industrial, etc)

D = Standard 23C four cylinder diesel engine

F = Single stage clutch (As opposed to the dual- stage clutch)

140043 -- manufactured sometime in 1959.