When GMC changed everything in March, 1955, they kept their 270 series 6 cylinders, but, unlike Chevrolet, the did not have a new V8 to trumpet. Fear not, the solution was close at hand, cross town at Pontiac. The "sorta like a chevy" 287 V8 with 2bbl carb was swapped into the trucks, and in 1956, the 316 upgrade was used. In 1957, the 347 CID Pontiac V8 went in, still with 2BBL, but a little parts swappin' would get a GMC what ran fast!. With GMC, they added 1 to the CID value, so the 287 became 288, the 316 became 317, etc...
In 1958 and 1959, they used a 336 CID version that Pontiac never had in their vehicles.
Buick V8's were used in larger Chevrolet Trucks, and larger GMC trucks used Oldsmobiles. All were modified for truck use.