As mentioned above, the '60-'62 frames are wider, than the '63-'66 frames, so it is not a direct swap, but it can be done. Before doing any cutting or drilling, set the '65 cab on the '62 frame to determine alignment, geometry and level. If you like the specifics, assess the cab mount frame perches, to determine if and what needs to be modified.
I hope this information is helpful and keep us posted on your progress.