What years can cabs interchange with '65? (Talking 1/2, 3/4 & 1 ton Chev/GMC here)
Anybody have a decent cab for sale with minimal rot in Washington state area?

64 to 66. 60 to 63 had straight A posts and curved windsheilds, and 64-66 had slanted A posts with much-easier-to-form windsheilds. If you don't have much money, you COULD use the earlier cab design, depending on how partial you are to the design.