283s were primarily passenger car engines in '57, light trucks (1/2-1 1/2 ton) got the 2bbl 265, which was also the base V8 in the passenger car. I have heard of '57 light trucks with "factory 283s", but beleive those to either be a dealer install, or possibly a special order made by someone who knew the right channels, or a later aftermarket swap. There is also the possibilty that they were late year trucks, as the way I understand it, the 265s were mainly leftover '56 engines that were only used until the stock was gone.
i wont say "they don't exist", but the 1957 Truck Shop manula only lists a 265 in the lighter trucks, with the 283 in 2 ton and larger, plus the Loadmaster 322 V8 (actually a Buick engine) used in the largest Tandem trucks.
