i have had both a '63 and a '62 C10. Here are some of my observations.
'62 was the last year for the X-Frame and torsion bar front suspension. So '63-'66 will not swap frame or front suspension. '62 rear end is a 3rd member drop out style. '63-'66 has the more modern style, does not swap internal parts at all, but may swap as a full housing/axle unit.
As stated above, the windshield, cab, and doors are different from '64-'66, but the '63 is still a match to the '62 on that score.
Other body parts, fenders, hood, bed, tailgate, etc.. do swap. Grills and grill surrounds do swap, but the grills are not physically the same as the '62. '60-'63 had single year production on their grills, different for each year. '64-'66 had the same grill for all 3 years, but different from the previous years.
Engines/transmissions can swap, but you need to be careful. If you have the I6 235, you will need to change the bell housing if you go to a later model I6 230/250/292 or a V8. The bolt pattern is different. Also different is the tranny mounts if you have a manual tranny. '62 has 2 mounts on the bell housing that are not there on '63 and later models which use a rear transmission mount.
These are just a few things I can think of off the top of my head.
Basically it boils down to "If you must buy a '63-'66 parts truck, get a '63. It is the best match of the '63-'66 series."
I don't think that rear trans mount was used on manual trans until 68. p/glides used the rear trans mount from 60 -66 and the t400 in 66
ron
