A GMC would not have had a 348, they ran Pontiac engines for the V8 option. There was, however, a 347 option for '57 (one year only option) in GMC. Chevrolet did not offer anything larger than a 283 in a truck under 1.5 ton until well into the '60s, and the 348/409 was never offered in a truck under 2 ton.
