if it's not a 283, and it's original, it's a 265.which was the optional V8 55 to mid 57 - the 265 didn't have the oil filter at the bottom back of the block like later V8s, as well as some other different details that slip my old mind right now - if it's a 283, the tuneup specs will be the same as any 57-60 283 found in any shop manual or motor manual, and in a 50 year old truck it's prolly been replaced sometime anyway
get some casting #s from the block/heads and we'll be better able to tell what ya got
Bill
