on the 1200 site someone quoted:
(You CAN use the early [front distributor] head on the later cylinder block as the oil feed to the rockers is pumped directly up the correct head bolt hole in the cylinder head.
You can NOT use the later head on the early block because the early block feeds the rocker oil to a small vertical drilling at the side of the cylinder head gasket face. The cylinder head needs a corresponding drilling that feeds the oil across to the same cylinder head bolt hole as the later engines.
Since the newer heads do not have the drillings necessary to pick up the early engines oil feed, the rockers will not get any oil at all with predictable results.)
Ive since checked oil feeds head seems the same , time will tell