To the best of my knowledge, 1957 to 59 half ton Chevy frame, axles, linkage, shock mounts, steering box etc are the same. Both have short boxes although the 57 is a stepside and the 59 is fleetside. Everything mechanical underneath should interchange. Does that sound correct?
J Lucas You will likely find that brake line from master cyl to rear axle assembly differ from 57 to 59. On 57 it crosses over to right side frame & back to rear axle. On 59 it goes back on left side to rear axle. FYI delky dave in wyo