You may be lucky and it is the head gasket, sometimes the oil pipe through the bottom of the rad can leak.
Usually it is the good old porous block, l have run Fords for over 25 yrs, had 3 go porous. lining is ok, but does not last, we used to bore and reline the blocks then send the tractor down the road. On low hours one's we have bought new short motors, and once a complete new engine