[concours] E-type - Question on 1967 Head Color

As you all know, the E-type had gold cylinder heads up until sometime in
1967. The very late cars had open headlights and unpainted heads prior to
the 1968 Series 1.5, all of which were unpainted as well.

Does anyone know at what engine number the paint was deleted? My car has
curly hubs and covered headlights, but it also has hazard flashers with the
cover. It was built immediately before the switch from a rubber gearshift
surround to ambla.

The head is unpainted, but it appears that the head has never been off the
engine, as the ridge, characteristic of a head that has never been skimmed,
is present. While I prefer the esthetics of a painted head, I do not want
to do so unless I can be sure it is correct for my car. If it IS correct
for my car, I do not wish to pick up deductions from a judge following the
manual, as I’m certain that at least some 1967 cars had unpainted heads.

Advice? Anyone know of the cutover point?
-Steve A.
'67 E Type Coupe
'76 XJ6C
'91 XJ40