I believe Chevy dashboards are basically the same from 1960-63 (double hump) and 64-66 was flat on top. GMC had a single hump on the driver side for all of 60-66, however the original cluster was a small gauge panel in the middle of a sheet metal pan, and the later version filled up the entire cluster area with a much better looking plastic assembly.
Here are examples of the four flavors:
1960-63(?) Chevy
1964-66 Chevy
1960-61 GMC
1962(?) - 66 GMC
Google Images is the easiest way to obtain photos of anything on a web search. Good luck.