As far as I know the body parts are interchangeable for all 61-66 Ford 1/2 tons. There is a difference in the craese that runs down the down just below the window. The early trucks are straight, the later (65-66, I think) have a dip in the crease about a third of the way back. There are, of course, grille and trim/ornamentation differences here and there.
The 65 was the first year for TwinIBeam suspension and this changes the steering somewhat. There are brake system differences scattered throught the series as well.
The '65-'66 cab is different, then '61-'64 is the same.
With '64 the steering column goes down through the floor between the brake and clutch pedals...or between the brake and accelerator, I forget. Then inner fenders and radiatore support of a '64 are also different from '65-'66.
The lines are different and most of it bolts up different if I remember right. Been about 5 years since I had a '65. BTW what parts do you need? I'm parting out my old '65.
Oh and check out <a href="http://www.ford-trucks.com" target="_blank">Ford-Trucks.com.</a> Lotta guys over there with '65-'66 Effies.