I'm going to guess the awnser your looking for about the GMC General will be in the book, "GMC Heavy-Duty Trucks 1927-1987" &/or "GMC: The First 100 Years".

I see 1976-1987 in one book and 1977-1987 in the other.

as for 6x6, well I guess if some one had a need and the money they could have gotten it that way......

1965 GMC 3500 Rescue in the Stovebolt Gallery

My Facebook Links:
Jolly Goodfellow.
the 6066 GMC Guy.
Jolly's Truck & Car Show Page.
Owner of ~ 1965 GMC 3500 Custom Rescue Squad {Black Built Bodies}.