Not a Bighorn or a Bison...
Actually either a LCF or a HCF Dodge (Bighorn's came later, are larger, have more integrated fenders, and had a MUCH smaller production run...).
LCF (or C series) was introduced in 1960 and ran until 1975.
For info, see:
http://www.olddodges.com/index1.htm and click on the C tab...
LCF stood for Low Cab Foreward...
Bighorn (CN/CNT9500),1972-1975. 261 built. I know the guy who owns the first one off the line (local ATHS member).
For more info, see:
http://www.olddodges.com/index1.htm and click on the bighorn tab...
I'd give more direct links to the pages if I could figure out how...
Oh, and if you take a gander at this site, they have some nice brochures and tabulated data on the LCF models as well.
http://www.sweptline.com/hist/bigtrucks.html
One other thing to note (asside from Dodge's using the pickup cab on these rigs giving the driver a really nice ride...) is that the fenders are hinged. Combined with flipping the hood up, you got very nice access to the engine (only the back was obstructed...). 1960-1966 they had dual headlights, single lights from 1967 to end of production (civilian models...).