Mine was actually a Blue Chip 550. It was titled as a 56, but it was born with a 370 engine that did not become available until 1957. The 503 was still available in the Blue8 Chip series in the 630. The 650 series had the Olds V8. Chevrolet then introduced the 348 and a little later the 409 which were also high RPM engines and dominated the gas market for quite a few years until the first oil embargo totally killed the market for gasoline powered trucks to gross 80,000.
https://plus.google.com/10819770718...4965267442&oid=108197707187186692269The engine was actually a 371 Olds engine with lower compression and rotating valves. The original carburetor was a Holley teapot which rated it at 232 HP. Not long after the picture was taken, I added a Neway drag axle to it. The intake manifold was actually Oldsmobile with an adapter to accept the Holley. I removed the adapter from the Olds manifold and installed carburetor from an Olds 394. I had forged flat top pistons instead of the dished pistons that GMC used. I actually pulled a grain trailer more than pulling a tanker. I got about 100,000 miles between overhauls and drove it about 125,000 miles a year. I made sure I never let the RPMs get below 3600 and usually downshifted at 3800. I up shifted at 4200 but letting her go to 4400 to get a run at the next hill was common. I averaged around 2 miles to the gallon loaded and about 2 1/2 empty, but gas was only 20¢ a gallon back then. Hauling a load of grain 250 miles paid about $125 in those days and it took about $25 worth of gas.
