If you haven't found this link yet, it may prove very helpful:

http://www.stovebolt.com/techtips/buyers_guide_60_66.htm

And the following link to a GMC site provides a lot of valuable information for both GMC's and Chevys of this period.

http://www.6066gmcguy.org/GMCvsChevy.htm

1960 GMC 1/2-Ton Pickup Truck
In the Gallery
Updates in the DITY Gallery
Now cruising in the Passing Lane