Dan,

64-66 trucks are all very similar. For a VIN decoder, try http://www.americanclassic.com/paint_test.asp. The only way to tell the small blocks apart is to check the stamped number on the pad on the front passenger side of the block, or the casting numbers. In '64 I think the only v8 offered was a 283, but it could have been switched.

I can't help with A/C.

Brian