http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=printview&t=3690&start=0 says there were about 500 made, so it's rare.. and this thread mentions one in San Diego. Gotta be this one.
Design of the 5-Ton M656 Tactical Truck
Document Number: 680101
Date Published: February 1968
Author(s): W. H. Kind, J. S. Logan - Ford Motor Co.
5-ton tactical truck M656, which will be used as cargo truck, personnel carrier, and prime mover for missiles and artillery. It was developed with an eye toward specific requirements which had to be met in the areas of reliability, durability, mobility, and ease of maintenance. Human factors incorporated in the design provide for ease of operator control, maximum driver safety, and comfort.
Reviewed in detail are factors considered in development of the powerplant assembly, cab design, drive train, suspension systems, and steering assembly. By designing the M656 from the start to military specifications, a new generation of tactical trucks was developed. By this direct approach the military was able to acquire a vehicle that had swimming capability, air transport feasibility, severe off-road operating ability, and extended maintenance intervals.