For the trucks, there are two ratings for each engine (three if you include "taxable horsepower").
For the 1960 trucks, the 292 MD (2 barrel carb), the truck operator's manual lists 172 hp @ 4000 rpm. This is "gross" hp. The number on the plate on the glovebox door (146 hp @ 3800 rpm) is a net hp, or what is available when the engine is installed in the truck with all accessories (air filter, generator, muffler, and so on). And the horsepower does vary with engine speed. The max torque of 270 lb-ft @2600 rpm gives 134 hp
Just for grins, the taxable (SAE) hp is listed as 44.60. Not related to power at all, but related to bore diameter and number of cylinders.
Thanks 3414, that actually clears the numbers up quite a bit. Now that my curiosity is settled, I can get back to the real task at hand which is unloading that dump body so I can put the truck into the garage and fix the brakes and sheet metal.