Section 109, page 31....
"Pumps with a 7.5 mm diameter plunger must not be installed on model FMD engines prior to serial 1425097"
You can put the 296 and 380 [p/n DD-993100-A, DD-993100-B]on later engines but you cannot put the later pumps [498 Ford p/n DDN-993100-C] on earlier engines. You can instal a pump other than original equipment but you may have to change other parts which is in the FM tractor parts list"
stiff cheddar.Are you sure there has not been other alterations to the motor.?