Virtually every part from '64-'66 are interchangeable. The cab from a '64 will bolt directly in the place of a '66, regardless of the wheelbase (long wheel base or short wheel base) or bed style (fleetside or stepside). Along with the bolt pattern/number of lugs, the VIN number on the top of the driver's door pillar will indicate whether the truck is a factory C-10 (1/2 ton) or C-20 (3/4 ton). If the VIN starts with C1546 it is a conventional cab (C), 1/2 ton (1), long wheel base (5), fleetside bed (4), 1966 (6). If the VIN starts with C2546 it is a conventional cab (C), 3/4 ton (2), long wheel base (5), fleetside bed (4), 1966 (6). If the VIN starts with a K it is a factory 4x4. I hope this helps.
