Hi and welcome.
There are 3 different types of door but it is fairly straight forward:
1 Up to '63
2 '63-'74
3 '74 onwards
The doors are the same but you need to ensure you get doors for 2 above.
The only difference is the glass winding mechanism between the 40 and 45 but this may not be applicable on all 3 types.
I think '63-'74 had quarter lights and the earlier ones (1 above) were slightly smaller. As to overall dimensions between your '66 and a 75 , that may well be the same but the early doors have thicker rear frames and, from what I can see, the skin profile may be slightly different, but that view is purely from looking at photos as I cannot find any reference/dimensions to confirm. Conversely it may well just be the internals that are different so if it possible to measure the '75s you may well be okay with them.
Not very conclusive, I'm afraid, but Mr T didn't change things unnecessarily so there is a good chance that they will be the same.
I'll continue to look and see what I can find.
Regards,
Rodger