You will need to do a little more research and tell us what kind of a tractor you actually have.
Ford did put a 4 cylinder diesel engine in the late 50s 641s but it definately was not a Perkins. Perkins were only used in the Fordsons as Sean suggests and they were 3 cylinder, not 4.
Here is a 641. It's a gasser but they look the same as a diesel.
Here is a Fordson Dexta.