1962. On the face of it no white wires, but close inspection indicates the wires are wrapped in black tape, and there are traces of white at each end (arrowed), entering the motor near the top.
1964. Definitely two white wires entering the motor at one point, near the bottom.
1969, still two white wires, although one has sleeve on it, possibly indicating polarity! This wire does seem to be going to the coloured harness wire, with the other one going to the black.
1972. Now one coloured and one black wire, although it isn't clear where the two wires are going on the motor. Compare the depth of the motor bodies in the following pictures with those above.
1975, definitely one coloured and one black wire going to opposite sides of the motor. A clear difference in the shape and size of the flange on the motor body compared to the earlier one.
1980. Probably the same size motor (externally at any rate). Three wires coming from a 3-pin plug, two of them going into the heater casing plus the black earth wire going direct to the motor, and a third coloured wire coming out of the casing and going to the other side of the motor.
1968 MGC. This seems to have the early longer motor and the two white wires, ...
... but this 1969 MGC seems to have the later coloured wires and the shorter motor, even though it is still three years before the introduction of the V8. However this, and any of the photos, could be sporting a replacement heater unit or motor.
Dropper resistor for 77 and later 2-speed heater fan (circled) inside case (Photo by Andy Charman)